What is my obligation?
FH and I have been together for 5 years. We moved in together after a year and after 2 months of living together, we found out about the existence of FSS6 (2 years old at the time). FH never had a relationship w/ BM; they had some mutual friends and ended up having a one night stand when he had just broken up with his then-girlfriend. BM contacted him when she decided that she wanted child support.
It's been 4 years now since we found out about FSS. It was very obvious from the beginning that BM didn't really want to be a mother and therefore doesn't put any real effort into caring for her son, leaving most of the responsibility to her mother when they're on good terms. When they're not on good terms, she finds whatever loser will have her and moves in with him, taking FSS with her. After the last time this happened, about a year and a half ago, FH stepped in and took over the bulk of the custody. FSS lives with us most of the time now.
I have never wanted children of my own and I made that clear to FH from the beginning. FH himself was on the fence about it. Learning about the existence of FSS blindsided both of us and we've tried to cope the best we can but it's been difficult, to say the least. I supported FH in his decision to take over more custody, though, and try to provide a stable home for FSS because it was the right thing to do for FSS.
The problem I'm facing now is that FH seems to expect me to be a substitute mother to FSS. This expectation has always been there to a degree, but since we got engaged last summer it's gotten progressively worse. I do my best considering that I never wanted a life with a child in it at all. I make FSS's meals, do his laundry, clean his room, keep up with school functions and doctor's appointments, plan his birthday parties, keep up with all the legal/court issues and documentation, and just overall help out FH and do my duty as the lady of the house. I try to be a good role model and treat FSS fairly, just like I would any child in my home. The reality, though, is that I do not love FSS. I say it back when he tells me he loves me and I play the part, but really, I don't like him at all. It's not his fault, I know, and I work very hard every day to never, ever let it show that deep down I just wish he never existed and that I could have my life back.
But just this past weekend FH and I got into a huge argument about what exactly my responsibility is when it comes to FSS. FH implied that not only was it my responsibility to make sure FSS got dinner every night (something I mistakenly thought I was doing voluntarily out of the kindness of my heart), but that I should be taking FSS on outings and doing activities with him on my own on a regular basis. He said that I'm supposed to love FSS. He made me feel like a horrible person for not feeling the way he thought I should feel about his son.
FH has gotten this idea in his head that I should be the mother to FSS that BM isn't. I think FH looks at me as a co-parent because I was around before we found out about FSS. But I am NOT that child's mother. Is it really my responsibility to make up for her apathy? Isn't it enough that I do everything for FSS? Am I supposed to force myself to love him? Is that required? How would one even go about that? Help!