Marriage problems

Hi all, after 27 years of marriage I am still struggling to forgive my husband of a fling he had 20 years ago. My older son is ADHD, so I had committed to homeschooling him. I was pregnant the whole time my husband had this fling with someone else. Yes, he was with her the whole time I was pregnant. Also, we planned to have our second child. I knew my kids needed me, and I really had no where to go. My husband wanted to stay together, and the only reason that I did was for my children's sake. I have hated him off and on throughout our whole marriage. About six years ago, he was texting with one of his female coworkers on a weekend, instead of talking to me while I was right there. It was flirty and non work related. When I told him it was wrong, especially since he was her boss, he exploded. We had a huge fight. We have been through so much together, but I think it is so weird the hot/cold feelings that I have for him. I have also noticed that anytime in my life I am really dependent on him, like recently when I had to take care of my parents, I feel very close to him. When I gain independence, he gets very nasty with me over nothing. I think the only way for us to have a good marriage is to go to therapy, but I know he won't do that. I know we both brought some baggage into our marriages from how we were raised, and I know this contributes to his behavior. I have never been disloyal, but he used to accuse me of that. He is so secretive of his stuff, but he wants to always see who I'm talking to. I just want peace in my life at this point, as an older person.