Am I an idiot?

Just let me start by saying I'm a 50 yr old divorced man with grown kids. For the last twelve years I've been seeing a wonderful woman. My firey redhead, I called her. We met at work, she was separated from her husband at that time. Had been for a year. We started dating and I fell deeply in love with this woman. We dated for 6 years, and in 2000, I bought a house and we moved in together with her 3 boys. All this time she was still married but separated. When ever I would bring up the idea of her divorce, she would get defensive and say no one could judge her that wasn't in her shoes. Eventually I quit bringing up the divorce thing, not wanting to upset her. In 2003 I tried to start a physical affair at work with another woman, because I was not, in my opinion, getting the sex I needed at home. Needless to say, that bit me in the butt and my live-in found out about it. She threatened to leave, but I convinced her I was willing to go to couples counseling if she was. We went to about 6 months worth, once a week. Things started to improve between us, and the sex life really heated up. She was willing to try new things and actually tell me what she wanted, which had been a problem.. Everything was going well. Then about a year ago, I noticed an increase in cell phone traffic between her and the husband. I mentioned this to her, telling her I was feeling uneasy about the more than usual communication between them. I also mentioned the divorce thing again, for the first time in 2 years. She said she wasn't ready to get a divorce(?), and that they were talking about the kids.Things went on a downward spiral from there. Communication virtually ceased. As did sex. She would go into the bedroom and watch TV and I would stay in the living room and do the same. The tension in the house was thick. Her 17 year old son started staying out late, because her and I were always arguing and he didn't want to deal with stress. I couldn't blame him. Then on March 3rd, I came home from work to find her and all her stuff gone. I called her, she said she had moved her shit out, she was just tired of the whole thing. I asked her if we could at least talk about it. She said yes, but didn't know what I hoped to accomplish or what I wanted from her. She said we should wait a week and then we could meet for lunch. The week went by, me trying to put the house in order, and get my shit together. When she pulled up at the eatery, she was driving the hubby's truck. My heart just went to my feet.To try and be brief, she had left and moved back in with the hubby. She said she cared for me, but that she didn't love me. Also, that she still had feelings for him. I guess I knew in my mind that there was always the possiblity that she would go back to him, but after being separated for 14 years, I didn't think it was likely. I've muddled through the last two weeks and tried to keep busy. My parents and my kids have been supportive and I am grateful. My mom asked me, that if my SO decided that she had made a mistake by going back to her husband, and wanted to come back to me, would I take her back? I thought for a moment and then told her yes. Am I an idiot?