First of all thank you all for replying to my post. I was at home with my daughter when I was writing it and she woke up so I hit save thinking I could come back to it, but that published the post incomplete. I was surprised to get so many replies to an incomplete post so thank you.

The plot is thicker than what I have posted, we have just recently purchased a house together and officially moved in. I had my own house until October and we moved into this house in December. I do fear the confusion this will create for my kids, the oldest was old enough to be affected by the divorce. In many ways I think this relationship has been closest to him feeling normal in terms of a normal family. That said I understand that me being miserable will make him the same. So change is tough but misery is worse.

I think part of the problem is that neither of us love each other enough or as much as we love our own children. I don't think I love her enough to sacrifice my kids and what I want to do with them because she has a son. Even sacrifices for her, this summer she wants to travel to her parents house, this will be at the same time as my daughters first birthday. I don't want to go, haven't said it straight to her, but my son is very good at baseball and will likely play all stars this summer. I don't want to sacrifice him doing that, or me going away without him and missing it for her to go home. For that matter I would sacrifice my daughters first birthday to be there for my son and for me. Perhaps other birthdays when she knows what is going on I would make a different decision however for the next 3 years I want to be committed to my oldest's opportunities, her time will come. TO me this is the decision any "normal" couple would make for their son. Or they would split the time, split the travel, and be ok with it because there are no broken allegiances. If I don't go and we are together I know I will be resented for it. It will be a huge fight, I will be told I put my kids first always. The irony is that yes I would be, but I should be allowed to and not have guilt associated with it. In turn she should be able to do the same. In fact she has, the house we bought is in a different school district than where my sons go to school. AS a result all school, sport teams and friends are split. We are not really a blended family. This decision was not negotiable because she believed her son couldn't take the change and she wouldn't do it to him. She always wanted to live in this area and had no intention of moving. She has many reasons outside of this as to why she wouldn't combine closer to them and closer to where we both work. She didn't want to share school events and have to see my ex all the time, have integrated friend groups etc. She also didn't want my son and hers to play on the same teams or in the same leagues as her son would be over shadowed by mine. It is true that my son is successful in sports, however my son is her sons biggest support club. When we go to his events my son sits in the bleaches and cheers, sometimes his voice is the only one you can hear across the entire filed. They both played football for the first time this year, her son cried and wouldn't go out on the filed in the first game. After that when possible my son would go with him to his game and throw the ball with him before hand, after which he wouldn't be nervous. They have been doing a once a week baseball clinic the last 2 months, when they have a competition in the clinic and her son wins mine is the first to go over and say well done and pat him on the back. If it is the other way around he her son sulks, life is terrible, and begins recalling all the bad things that have happened to him in his life, like some teacher was mean to him 3 years ago. It makes me proud when my son does this, it makes me sad for my son in that it doesn't happen the other way around. My son and I are tired of celebrating her sons mediocrity. We have to celebrate when he argues his way through trying spaghetti. My son congratulates him, but made a comment that he is amazed how good he is at everything. Obviously tired of the praise for something 99% of kids just do.
His disregard of my youngest hurts him greatly and makes me hate the SS even more. The first summer we were together the SS was an 8 year old living as a 6 year old. Still made pretend cars and planes with shipping boxes, still played make believe game of killing zombies or pretending to be power rangers. My youngest was just 5 years old and this was heaven for him. My oldest would grow tired of this quickly and come inside and watch TV. Everything changed when the SS played his first year of kid pitch baseball. He suddenly lost interest in the child like games and wanted to play sports or watch sports. My oldest was happy, my youngest was lost. He would ask and ask or him to play these games and he would turn him away with disgust. He then would not sit on the couch near him, slam the door and lock himself in the bathroom if he got in there first for cleaning teeth. Lost his mind when they were playing in his room and my youngest climbed up on his bunk bed. Meanwhile his mom is protecting his "space" and saying he is allowed to have his own time by himself. He would use this to escape from my youngest but secretly make plans with my oldest for him to come play with him. I shut this down quickly, but she continued to say he could go to his room and play by himself when ever he wanted. He knew this and began to use it to quit things when they weren't going his way. He is the kid that throws the bat and storms off by himself when he doesn't think he is out. Makes up new rules on the stop etc. Starts telling me Mommy said I could play in my room by myself. Would quit even in the sports he liked, when he got to do the thing he wanted and then wouldn't turn around and reciprocate for my oldest. This would drive me crazy and I would complain, she would say he doesn't have to play if he doesn't want to, I would say this is a total douche bag move, she would get offended cause I couldn't talk about her son like that. Now we all have to ask permission before we touch anything of anyone, he will say no you cant use something of mine even if he is not using it. HE would rather play xbox by himself, sit and watch my son play his 30 minutes, then play both sides of the game by himself, make sure the game goes into overtime and get to play on past his 30 minutes.
So don't get me wrong I have invested in this kid. Make sure he has a gift for his mom for all occasions. Looked after him while she went to the gym, went to his school stuff, tried to teach him to throw as he was hurt he didn't get to pitch in Little League when he couldn't get the ball to plate. You cant teach someone that doesn't want to listen.
We travelled overseas to say my parents who are ill. We took the baby but not the boys. We flew her mother in to look after her son so he didn't have to commute to school from his father's house while we were away. While we were away we organized for SS to sleep over at my kids mother's house so they would see each other while we were away. Has never slept over before, has friends to his house but is too insecure to sleep somewhere else. This was a perfect opportunity for him to be somewhere he could be comfortable, sleeping in the same room as his Step brother should be fine right? Get call from ex saying grandmother said he doesn't want to go. Discuss it with fiancée and she suggests getting my son to call him to convince him to go, this is an important opportunity for him to get some confidence. My son calls talks to him, he says he will go, grand mother gets on phone and says he shouldn't go and wont be. Get call from ex again. fiancée says nothing she can do as she is not there. I am furious and try to deal with it with prayer, acceptance but am just pissed at everyone. Mad he is so flimsy, mad grandmother interferes, mad fiancée washes her hands, mad that my son gets disappointed and feels like these things always go one way with him. Have heard my oldest say things like.... he come over here and check out what I just made..... no never mind I know you wont....
He has resigned himself to it, but I don't think a 10 year old does it with acceptance, I think he starts to think that this is normal and you know what I should do it too.
I find it increasingly difficult to differentiate between my oldest growing and nearing puberty and his adoption of the attitude and intolerance exhibited by SS. He has become far less tolerant of his younger brother, mean and spiteful. This was the nicest most caring kid you would meet, evidence in the baseball example above, just a giving kid, then all of a sudden he becomes nasty. It may be hormones but I cant help thinking that it is a combination.

It think I have realized that I am just not ready to be someone's step dad. I also am not ready for some one else to be a step to my kids. I am just learning who I am, I make these discoveries on a regular basis, it is so hard for me sometimes to know what I think or have an opinion on anything because I just don't know. Not having alcohol in my system changes my perspective. It is actually like everything I have learned is erased and I have to develop ideas and opinions and values all over again. Without the tools to survive I just react and don't really know what I am reacting to, but my gut says no, then I have no way to explain how I feel or why I feel and it just ends up a fight. I know that love is not enough, I know that I can survive on my own, I don't know if I can survive where I am.

With regards to breaking the first rule, yes I did. At the time I didn't know there was one. I was sober for 6 months before I got a sponsor. I didn't know how to ask someone, I went to meetings where I wasn't being told to get one. I was on cloud 9, free of the previous relationship, my body cleaning out and giving me energy and life, I immediately spent all my time with my kids, I apologized to my ex. I found this new girlfriend and life was good. Pretty soon the shine wore off. Relationship issues came, the pregnancy came, my brain was going to explode, I finally could not stand the madness anymore, I would break down in meetings crying like I did when I first arrived. My sponsor found me. I am still working the steps, having disengaged mid way due to life and schedule and thinking I was giving to another by not going to meetings. This was wrong, this is why I am where I am today.
The hardest thing comes now that I have to have the conversation. How do I do it without a fight. HOw do I say I don't love her son and cant be around him, that I wont sacrifice for him at the expense of my own?

She wants date night tonight, told me she likes roses and love notes, I am off to buy the food I will cook for her!

Wish me luck!

Thank you all for your replies. It is good to know I am not alone or crazy. That said I spoke to my sponsor and he asked me am I takng the easy way out. I have to say this didn't feel like support at the time however I am going to do what I can to try to be honest about how I feel more often. It is still hard, very hard, in fact today and last night I was tested by him and his attitude yet again. I am commuting to the two of us going to counseling where hopefully I can express some of this in a safe environment. We have been before but stopped when the benefit ran out. Sometimes I feel like she didn't like what she was hearing from the counselor before. But I will give it a chance again I guess. I am trying hard to be fair and equal with him but it is so hard. Oh so hard