My only suggestion would be working on yourself to get to a point where you're happy that he's happy. The whole concept of compersion is very interesting and attainable with a little work, I believe.
I'm a pretty needy person when my husband isn't at work. I am currently a homemaker so when he isn't working, I want to get out and do stuff. When he has another interest, that takes time away from me that he usually dedicates to me 100%. Do I struggle with it? Yes, but overall the fact that he is happy and getting to do something that he enjoys (whether it be dating or some activity that I have no interest in) makes me happy so I just use the time to do things he doesn't enjoy doing - watching tv shows he doesn't like, listening to music he doesn't like, etc. I usually end up enjoying the time immensely and then when he walks in the door with a grin on his face, it makes me look forward to the next time that we both get to do something we love without making the other one suffer through it.
I'm sure it's a little different with a partner that you don't live with, but I think the concept would be the same: Try to get to the point where you're happy for him and focus on how the situation benefits you.
If it's a situation where you aren't happy and don't think you ever will be, that is something serious that needs to be addressed. Either by figuring out a way that you get more time with him or by ending the relationship if you two can't work out something that satisfies you both.