I'm sorry for your situation. You mention "kids," which makes this more complicated. The good news, as I see it, is that you have already survived a year of separation. I think you're going to have to write off these past 3 months as a failed attempt to save a marriage. You tried, but it is just not working. I don't believe it ever will.

It's getting these days to where being diagnosed as Bipolar is being used to cloak any multitude of problems/failings. You can delude yourself into believing that the main problem is his supposed Bipolar Disorder. It's not. He has a kinky-ish sexual orientation. He doesn't just need "spice," which you can provide. He needs more than you're ever going to provide. And he is not going to stop looking for it. Instead of taking this to mean that you are worthless, take it for what it really is: There is something seriously wrong with him, and I'm afraid it's hard-wired. He's damaged. There is no medication that fixes his problem. He's to be pitied, but not to the point that you sacrifice yourself on the altar of trying to make work what is unworkable.

So you were like 17 y.o. when you got involved with him. He was 25. From what he says, he knew, even way back then, that he had this drive. You are only more recently finding out that he is this disordered. I don't use that word to make a moral judgement about him. I use it because he himself describes these tendencies as "battling demons." It's not a happy way to live, which is why I say he is to be pitied. I expect that life is going to get worse and worse for him, no matter how much psych treatment he gets.

The main problem is not that he is attracted to sexual contact outside the marriage. The main problem is that he does not find much sexual fulfillment inside the marriage. That's what gives you so little to work with. Well-adjusted people manage to meld together sexual satisfaction with love. He has those two things completely separated. There is no having any satisfying level of intimacy with someone like that. Stay in this marriage and you have a life of loneliness to look forward to . . . worse than the loneliness of actually being alone.

Another piece of good news is that you are all of 24 y.o. Get back into that separated mode that you were in for a year. Then start pursuing divorce. Don't be real mad or bitter toward him. He didn't chose this orientation. He's screwed up. Don't tell him that "If you really loved me, you would change." Who knows what we can and can't change about ourselves. All that you need to focus on is that you need to change your living situation, and manage that change to be as non-stressful for your children as possible.