What should I do I found out the reason I believed the ex was extradited back to California isn't it.?

Friday I did some researching after my fiance' urge me to check and see. I thought the ex was extradited back to California for back child-support and I found out on my own it was for Laud conduct with a child and possession of a control substance. My first reaction when I found out the ual charge was to keep our kids away from him. He's been in their lives all their lives and I never had any suspicion that he could do this. He hates child molesters. Part of me wants to believe it's a misunderstanding. I have heard of where ex's get mad and make false allegations or the kid gets mad. But he had 12-13 years to tell me, especially when we got a marriage license, that would of been the perfect time to tell me. I don't care what his excuse is he had to of known and he should of told me. This makes him look guilty in my eyes and others. I even asked him if child-support was the reason he was there and he chose not to be honest with me. I am upset that he didn't tell me. This is far worse than any lie I have told him. The rental office might use this for grounds to take him off the least. I hate to do it to my kids but I really don't want him around them anymore because I won't know what the real truth is and I am not willing to take a chance. I thought about supervise visitation if he gets out and makes it back to the east coast. I am so confuse now and hurt. Please tell me what you might do in this situation. I hope I gave enough details.