Ironically...
Ironically, my grandfather is in the same situation. He became separated from his wife (gram) in 1989, but lived with her until 1994... He had a girlfriend that passed away, then a while after that got another girlfriend (Timmie) who just recently found out that he was still married to my gram. She's a little upset (understandably because she was never told ... and now wants to make him get a divorce and marry him. (I dont agree with it because that late in life when his gf is younger, i think my granddad has found a gold digger but whatev)
POINT IS....
marriage is just a legality, I think you can trust him. People who have been married once or twice before really do learn from failed marriages. If he didnt tell you he was still technically married to his wife -- that sucks but its understandable -- could you imagine being in that situation?? (found a guy you really like -- and had to tell him you were married but in the process of getting out) it wouldnt look great. I think he has the potential to be a great guy! GOOD LUCK!
Hunter S. Thompson once said "Buy the ticket, Take the ride."