It sounds to me like he is telling you he wants to have his cake and eat it too. In other words, he isn't promising to be faithful, quite the opposite. He's saying he likely will pursue other women in the future.

I wouldn't keep this from his parents. I'd be matter of fact about it. That he wants to have sex outside the marriage and he is interested in dom/sub relationships--I assume he wants to be dom?

For me this would not be a marriage. It would be saddled with a horny boy who never grew up, and who feels no reason to do so.

I suggest you start looking into making a life for you and your children that includes learning what healthy self-respect is. Counseling for yourself is a good start.