What would you do?

I am a divorced mom with 3 kids. I met a man almost 2 years ago who has full custody of his son. At the time, we started as friends but at some point over the last 2 years things progressed and we started dating. Ive also known his son for 2 years now. Things have moved very slowly which I've liked. But To this day, we have never spent the night together when kids are around. And our ability to spend time together is very limited due to his child. His son doesn't like him dating and requires his dads constant attention. If the dad and I want to watch a movie he must sit in between us and also must choose the movie. If not, a tantrum will occur. He has sabotaged dates by stealing his dads wallet, refusing to listen to a babysitter etc. The son has also flipped out if I'm around and his dad holds my hand. The child (12) is not well behaved in general. He is an only child who demands to always have his way and must be in control of every situation. If he is told "no" or does not get his way he often throws a major tantrum including swearing, threatening, throwing things, physically harming his dad, and I've witnessed him punch his dog and hurt her intentionally when not getting his way, etc. This seems far beyond normal acting out. The dad had had the child in counseling for several years and the child sees a psychiatrist and is on medication but nothing has helped. This man is wonderful to me. Sweet, caring, supportive, understanding etc. However, I have difficulty liking his child due to the behaviors, my kids like him a lot but don't like to be around his son, and honestly I don't see a scenario where we could have anything serious due to his sons behavior. I just can't bring chaos like that into my kids lives. My kids are by no means perfect. But never have the treated me the way this child treats his dad or hurt their pets. The problem is his dad is wonderful and I feel like I'm letting a good man go. But then I also think it's been two years, and I'm wasting years on a man who I can't have a serious relationship with because of his child. What would you do?