He shouldn't have let you move in if he wasn't prepared to be a family with you, and your son.
But... your comment about your son needing a father - it just doesn't sit quite right with me.
On the one hand, I do think he shouldn't be with you if he's not prepared to be involved.
But on the other hand - it sounds forced. Like your priority is to find a father to make up for his missing one.
I think of my fiancé as becoming a family member for my daughter - not becoming a father for her.
Sounds like he works 5 days a week and you work 2. I wouldn't want to be getting up early every weekend to go to an activity I didn't want to do.
Have you explained why you wanted to do it? Does he know it's about bonding? Does he agree that's necessary? It may be he would commit to it if you both saw it as a necessary step. But why do you? You already said that your son really likes his stepdad. So if the family time is because you want to push a bond the other way, your boyfriend to your son, then the most effective way isn't pushing your boyfriend into something he doesn't want to do.
I know you've been with him 5 years, but you've only moved in once your son was 11. You can't drop an 11 year old in and expect everyone to feel like father and son. I think you need to adjust your expectations because they can have a LOVELY relationship anyway.
Oh and... why have you made yourself financially dependent on him? 