I am caucasian and husband african american why did he cheat after 11 years w a stranger, latino?

I was going thru a hard time emotionally I am 41 years old and my body is changing and I felt depressed, unwanted, unloved, and unappreciated. Back in November I noticed my husband started changing: staying out of the house, going out a lot, hoarding his phone, wasn't talking to me much as he used to on the phone, cared about what he looked like when he left the house, went to work early, lied about money, our sex life changed he wanted sex every single day. Well, back in November I decided to check his phone records and saw that alot of pictures, messages, and calls coming from the same number I confronted him and he was honest w me and told me not to call and start anything w her. Of course I called and gave her a piece of my mind and then he got upset. I wanted to know where they met, how long it was going on, how many times he had sex with her, why, what she looked like, etc.....Well, she was 10 years younger then me, met her at a bar, and that they only had sex one time the rest of the time they just talked on the phone about "our " life. He said she was just "cool". I just cant wrap me head around why you would meet someone at a gas station and or bar and why you exchanged numbers and talked to her for 4 months and have sex and not feel guilty about it. The worst thing of all that he disrespected me by sharing his thoughts and expressions with a total stranger but if that isn't bad enough her *** was nasty and had a STD and of course I got that too. He said that he would never talk to her again or cheat again. That he never meant to hurt me and that she just was cool and made him feel good about himself. I don't get that I love my husband I do everything to make him feel good and I can tell you the sex is so good that his toes pop and he calls my name so I know it wasn't about the sex. So why did he do it???? I am in no means ugly or fat. I found myself to be a very attractive, intelligent women with class. I just don't understand why he would want to be involved w a ghetto, bar hopping whore, that carries STD's.