And she is your fiancee why? Time to make a plan to get out.

And, you stay in this so-called relationship, why?

Get out! The child is going to grow up expecting everything to revolve around them bc thats what the parent is doing. If you dont want to come last (which you shouldn't) you need to leave. 

Are you the BF or are you the child ?   You know where you stand, you know her rules.  You know what you have to do. 
 

Personally. I could not live like this.  But that me.  I sleep with my So, with out the kids in the bed 

You are not the fiance. That is just what she tells her coworkers. You are in both their minds 'the guy living in the house who is the live in Maid, Butler, Cheauffer, Delivery Person, Cook & Waiter. '

Figure out your finances, find a place, and move. Say goodbye to this toxic relationship. You deserve better. 

Wait!? Your not allowed to sit in the front seat!? Your not allowed to sleep in bed with your fiancé Incase the kid wants to sleep there!? 
WHAT THE ACTUAL F$@!

why on gods green earth are staying?!
Get out! Run! Fly! Whatever, just pack your shit and get away from that! 

Jesus, everything about this sounds bad. Like, you have all the worst aspects, and nothing good that i can see. Even if your fiancee improved on half of them, it's still really bad and idk how you could get past knowing she treated you that way. 

It doesn't matter the reason why.  If you describe your relationship in this manner, "Pure crap on a stick on a hot & humid summer day," it is clearly not the one for you.  It would not be fair to anyone for you to stay in such a relationship.  I know it is easy for bioless current or future step-parents to get snowed into thinking that something as bizarre as you stated above is somehow normal, but I can assure you, NO!, it is not normal.  It is some manipulative, controlling BM thinking she owns you, and that is putting it nicely.  She thinks that she and her dear-child are so-o-o special that they get to have their cake and eat it too.  Meanwhile, you, her soon-to-be husband, gets to settle for whatever scraps BM (and eventually SD) cares to toss your way.  Now, if you want that for the rest of your life, then by all means marry her.

By the way, this is abuse, “I am not allowed to wear my ostomy bag any other way than what makes THEM feel comfortable.”  One day when they are all out and about, leave a note, and move on.  You are truly better off by yourself than you are contending with this particular BM and future mini-me-BM.   It sounds to me like at one point this set-up was just a convenience for the both of you that may have worked at the time, but now neither of you can stand each other.   

Dude! Really?

Make a special ops run to repossess your balls and GTF out of there.

You are the live in man servant and you don't even have benefits.  

What the hell are you doing?

There is nothin redeeming about this toxic shallow and polluted gene pool breeder and her pelvic sputum of a daughter.

Leave.

Please.

this has to be fake. what type of man would put up with THAT? come on.

Assuming the majority of the posters here are women, you've heard from other women that what your woman is doing is wrong. Neither one of them respect you and have no problem shaming you. The reason Fiance doesn't want you sleeping with her - so your SD can have 'her' spot - is a lie. You know what you need to do.

I'm so sorry you have to deal with these things.  You deserve much more and this is no kind of relationship.  I hope you can feel empowered to leave; seems there is no benefit, support, or respect in this dynamic for you. Obviously your fiancé loves you or she wouldn't be with you, but she obviously has no self-awareness or understanding of respect.  You should close the door on this chapter with your head held high and never look back. She will regret it, but it won't be your problem.  

situation and you are being taken extreme advantage of.

Since she places her daughter on a pedestal above you and the relationship, I'd let them have each other full-time.

Is her mother married? Maybe she's who you should persue? I'm kidding, of course, but so many women out there would LOVE TO SNAG A MAN LIKE YOU with NO KIDS. You've got a lot to offer a woman, just not THIS ONE. 

Go where the peace is. You'll be an awesome catch for a woman who can love you and appreciate you for who you are and what you bring to the relationship.