DH hasn't stopped working, but can at times step away from his work to do things with SS. My situation is the same, except I'm more accessible to SS. The homeschooling for preschool is not very intensive or time consuming. It little short bursts of school work mingled in with free play and such, so neither one of us have to sit with him for 4 hours straight.

We do not have a babysitter and I did not sign on to be a full time nanny. I was fully aware that DH had full time custody. SS would spend some weekends with his grandparents and was attending preschool during the week. All that changed recently and now SS is here 100% of the time and that's why I'm at my wits end. I just do not know how to deal with the chaos a 5 yr old can create and how relentless the attention needing is. I'm aware that I may need to pick up a new hobby to get some me time lol

Yes! I agree with you on this. DH on the other hand does not want his son in school for reasons that he sees as valid. I have suggested that we even use a day care for one or two half days a week and it's fallen on deaf ears. We do take SS to martial arts class two evenings a week, but I feel that isn't much in the grand scheme of things.
Being a step is such an awkward thing when making the final decisions on raising the kid(s) as ultimately the decisions are made by the bio parents :/

DH and I had this talk on Christmas Day... bad timing but oh well.

Christmas Day was probably the worst I have ever seen SS. We had Christmas morning at home, just the three of us and the dog and kitty. It was reasonably ok, ss was 100% focused on his things and very wound up. We then went to visit with DH's family at around lunch time and SS just turned into some crazy, selfish, rude, out of control other child. It was not pleasant at all and I very much detached from SS and enjoyed talking with others. I could see in others faces a few times that they were either irrupted or shocked by things ss would do or say. He would snap/grab a present from someone as they gave it t him with an angry facial expression and body language. He'd rip it open and then ask where the next present was Then he'd play very roughly with things he'd been given. Then find something else to open and so on. He'd do anything to be the absolute center of attention. I felt bad for the kid really, it did not seem like he was truly enjoying himself at all. Anyway, DH said that he just let SS do his own thing because it was Christmas and he didn't want to discipline him in front of the others and make any uncomfortable. IMHO we were all uncomfortable with the crazy behavior as it was and maybe discipline with have been a welcome relief after SS got through his screaming crying and sulking phase.

But, I still didn't comment about SS to DH. I wanted some sort of peace and knew an talk about it would not be right until we were past the holiday. But DH started commenting to me, in the car going home, about how distant I was from SS and why didn't I play with him or get involved with him. I just said that he was getting plenty of attention from everyone else and that I felt he was wanting all the attention from his family and tried to let the conversation fade out. So long story short:
DH brought it up again later when SS was in bed and we were relaxing. DH was disappointed with me for not engaging with SS. I said I just wasn't caring too much for the mood ss was in and chose to stay back a little. I told DH that I do need to have a break from SS once in a while and that doesn't mean I hate SS or don't ever want to be with him. DH said that SS will be with us 100% of the time and that's final. So I flat out asked him if he (DH) even wanted to be alone with me for 2 days a month and he said 'No", he wanted SS with him at all times and that when SS is in bed at night was enough alone time for us. I then said that I respect his honesty and respect his wishes and that I also respect myself and my sanity and my needs too and that we simply could not make this work anymore. I was also very hurt that DH simply does not want to spend 2 days out of a month with me alone... very hurt!!

So after many more words and lots of tears DH said that he just reacted to my request out of anger that I wanted SS to be with a sitter/family for a few days a month and that he didn't mean what he said. He begged and pleaded for me not to leave him. It was just a mess and so horrible. How it all came to that is beyond me, I'm still in shock and still hurt. DH is hurt too as he had/has what his ideal family life is like and it's not working out that way. He is the type who wants to make everything perfect and have everyone get along all the time. When he can't 'fix' it he doesn't know what to do.

Anyway, there was no grand exit on my part. I'm still here and we are still talking about this. We are both mentally and emotionally exhausted. I can't talk, think or feel anymore right now and need to take a few days before we come to any decision.

epiphany, I can't tank you enough for suggesting to straight up tell a kid kid when they are being annoying or interrupting or whatever. DH and I had a productive talk after I read your post and we agreed to try and let ss know these things before either of us became irritated or stressed. By doing this within reason for the past two/three weeks I have noticed an improvement with ss.... can't fully believe it.. but there is a very noticeable improvement all round. DH is loosing his temper with ss less by acknowledging unruly behavior before it escalates. I am more at ease with being more verbal when ss is beginning to get out of control and ss is starting to even correct himself at times and appears to genuinely apologize for being an ass lol. The yelling, by DH, has become less frequent. SS has less crying tantrums. Me; I think I'm more tolerant.
DH has in the past, and only once recently, been at breaking point over the fact that he feels like he doesn't even want to 'hang out' with ss at times... this in itself is a very positive step forward.

It's not perfect these days.. but what is?!? But any improvent towards harmony is very welcome. I imagine that this journey, for all of us, will have plenty of ups and downs. So long as the ups can outweigh the downs!!!

We have been working on the interrupting with good results. And also trying to show ss that 'silly' interruptions are just silly. He does have a habit of being overly comical to get attention.. even negative attention at times. So our tactic is to remain neutral when he tries to get a negative response. It's starting to work and we are seeing good improvement with less chaos.
Pretty much 24/7 with a 5 year old is trying and can be exhausting in a way, but I feel like we can figure it all out and deal with the crazies for the most part. Our parenting plan is to be consistent, direct, calm and unemotional when things get out of hand. It's not easy and takes a lot of effort to remain calm at times. We are also trying to be clear with explaining things to ss. The temptation is there to over talk situations with ss when letting him know what he did was not acceptable or just plain poor manners, so we are making a serious effort to keep things simple and short.

I came from being single and living in peace and quiet with my kitties on a secluded farm to the chaos of living with a toddler.. didn't know what had hit me and reacted badly by trying to keep it all in :O I have learned that even though it's never pleasant to talk with DH about how ss drives me nuts at times that in the long run it is better to get it all out in the open. Communication is not easy when feelings can be hurt, but once the initial shock or defensiveness wears off and the conversation can be discussed again that things are easier to work out.