My ex husband....

My ex husband and I have two kids, a 5yr old and 2 yr old. I'm currently fighting for sole custody. I'm 29 and he's 35. Ever since we divorced which was last yr he's been sleeping around and having flings and I guess refunding his singlehood or something. We'll today I've found out through a mutual friend that he's been seeing a 16 yr old! Normally I would love to use this information to get sole custody, but after seeing so many 'age is just a number ' posts on here, I'm wondering if I should just leave that part of his life alone. I don't feel comfortable with a 16 yr old girl around my kids though. But I rly can't use this in court, age is just a number and so many people support underage kids on here to have sex and live there own lives then I seriously can't judge this. No he is not a child molester either, again age is just a number apparently and even if it's against the law the over census of morals favors what I've stated. But I still find it screwed up and don't want my kids in that situation.

I'm stuck. Should I walk the high rode or send my ex husband to jail over something that isn't all his fault. (It take two to tango if the 16 yr old is old enough to have a sex life she should also be old enough to make her own dating choices)