You are being unrealistic if you think that several months of experiencing this situation is going to resolve it. Remember - this is a very young child and you are expecting an awful lot of him. It sure doesn't sound like this situation is going to work out. You're not ready, nor is his father, to be managing this together yet. There's much work to do.
my hubby and I have been together for 5 years, he has a 13 it old son and 8yr old daughter, two different mothers. his oldest I think hates me still his daughter loves me though. it took his daughter almost a full year to come around. it's tough on kids. we have a 3yr old and a baby on the way that the oldest already doesn't like. you can't always win step kids over.
I'm on the other end. My oldest son hates my fiancé and constantly tells him to get out says and does harsh things. Eventually it does pass, i have been with my fiancé for almost a year now. Don't expect the worse of the childs mother whether she is or isn't saying something. You have to show him your awesomeness. And make it very clear to him you are not there to replace mommy. That was always my sons biggest fear was ryan was replacing his daddy. Once we made it clear to him ryan was his friend that he wasn't required to call him daddy he eased a little. Try initiating with him playing with him, chilling with him. He have video games? Play even if you have no clue what your doing. My son loves zombies ry had no clue how to play zombie games but caught on quick to ease the situation. And yes I'll tell you it gets annoying hearing that your ex would do something so childish to ruin your happiness by using your child. And it is annoying to hear every two seconds that a kid hates you. Kids don't hate, they test the limits and when they don't understand something they simply refuse to accept it. How old is he?