Sloppy seconds dilemma

My boyfriend repeatedly chooses his friends over me when he has the opportunity to hang out with me. Every once in a while is understandable but here's the caveat. This weekend he asked me if I wanted to go out with him by ourselves (which we haven't done in at least a couple of months). His girls are with us this weekend and my daughter is with us all the time so he had asked his mom to watch all 3 for a few hours. Well then this week his friend's brother is having a bachelor party and he wants to go. So I told him to do what he wants. He's like I don't want you to feel like I'm dumping my kids on you but I do want to go. I said that was fine that I will watch them (which I don't mind usually) but I also told him that if he chose to go out with his friends then we wouldn't go out Friday night. Mainly because Sunday would come around he would realize he hadn't spent any time with his children and would at the very least talk about them incessantly when it was his fault to begin with. So once again I'm in a tough spot, frustrated, and feel like he doesn't want to spend time with me. I could tell him to not hang out with his friends because he already made plans with me. But I was hoping he would make the choice to hang out with me by just saying "do what you want". I knew that would be a stretch. So this is like the 5th time he's left his kids with me over the last 6 months. He's only watched my daughter once for a couple of hours during the last 6 months so I could do something with my friends. He says he owes me but frankly I don't think owing me should be watching my daughter in return but actually making time for me! But how do I say this without sounding completely selfish?

This whole situation is getting old and I can't figure out why I put up with it because I hate being the person to hang out with because he doesn't have something 'better' to do or someone 'better' to hang out with. Am I being unreasonable? Help!
Sloppy seconds dilemma
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