Boss is confusing me....

Here it goes, I've known my boss for 6 years and it's always been a strictly working relationship. I went through a divorce 4 years ago. My ex left me due to his controlling issues, only seeing me as a mother to our children, and he was 40 and said he wanted to be free. I spent 3 years in therapy and learned to love myself again. During all this, my boss and co-workers were extremely supportive and understanding. I've dated over the past 4 years on and off but am truly happy with who I am and where I am in life. My only missing piece is finding that best friend, partner. Approximately a month and a half ago my boss started texting me about work related issues, call me on the weekend to ask me a question on a file (that I know he should know the answer or could of waited until Monday), etc. now, we all play practical jokes at work on each other and know about our personal lives, families, etc. Over the past month he has sent somewhat flirting messages to me. He is married with two kids. His kids come to our office regularly and of course spend the day with me, coloring, going to lunch, everything. He has started staying at the office if I need to stay late to finish a task. I point blank asked/told him what he was doing, you're married with a family and he has a lot to lose. His response to me was that he's unhappy and he's stays for his kids. He cannot imagine living one day without seeing his kids. His wife has changed (she's on medication for depression, bipolar disorder) but she's a good mother. She nags him constantly for the long hours our company requires. According to him, this began about a year ago. Now, everyone at the office, including myself, thought he had a great marriage. I think he is purposely arranging schedules at work so it ends up being just he and I working late. I have advised him he needs to do what will make him happy in life. He tells me 3 days ago that he cares and respects me, but he felt I needed to know that over the past 2-3 months something has changed. His feelings for me have changed. He likes my confidence in myself and the way I can be a lady but on the flip side I can be one of the guys and hang out. He tells me that in 19 years of marriage he has never been tempted until I came along. I have kept him at arms length since he has revealed this. He regularly tries to call me after I leave the office, text me or will call me on weekends, always before he gets home or when his wife is gone. I have no idea how his wife is clueless to all this. His appearance has changed over the past 2 months, his attitude, everything. I feel for her because do I think it's an emotional affair at this point, yes. We do have long conversations about him, his life, my life. My problem is, I have always had the upmost respect for this man. Have I over the past year wondered what if he wasn't married, yes. Have I ever acted on it, given him any impression of my thoughts, no way. I treat him the same as everyone else and the same I did 6 years ago when he hired me. I guess my dilemma is, why is he doing this? If you are so unhappy at home with the exception of your kids, why stay? He tells me he has no regrets or guilt over his feelings for me. I don't understand it as I've never been put in this position. Reporting him to our superior is not an option. He would lose his job of 20 plus years. Any thoughts?