Personally, my thoughts would match what others are saying. But let me try to put this in a different perspective that may help.
He is telling you that "maybe" you two can be together after his 14 year old daughter leaves the house. Trust me when I tell you, if he and his wife are having problems that caused him to go outside the marriage, his 14 year old daughter is more aware of the problems than he may think. She will not be traumatized by her parents splitting up. He is feeding you a line that you are buying. So may I suggest asking him two questions.
1. Why do you need to wait for her to leave the house if your marriage is so terrible? Wouldn't your daughter be better served seeing you in a healthy and thriving relationship as opposed to the kind you claim to have?
2. When you say you are waiting for your daughter to get out of the house, does that mean in 4 years when she is ready for college or does not mean not until she is out of college and fully on her own? Putting it another way, are you willing to wait 4 years, until you are 53, to find out if he is going to honor what he is telling you? (And you did notice he said the two of you "could" end up together.) Give up 4 years of your life waiting for him if you want, but it sure isn't what I would suggest for you or anyone in your situation.
3. How exactly is your daughter so fragile that you don't believe she can handle a split between her parents? After all, millions of kids younger than she is seem to handle it well and grow up to be normal adults.
Personally, I'm not sure why you would think so little of yourself that you would allow him to use you as he is doing. EVEN IF he is in love with you, he is still using you. Your friends tell you that. And now a lot of total strangers who have no stake in this are telling you the same thing. Don't you think maybe, just maybe, everyone is seeing things a bit more clearly than you are?
I made a mistake posting here.
No, your mistake was getting involved with a married man.