Learning to trust again.

I have been with my husband over 20 years now, I am 31 years old and he was my first boyfriend so he’s all I’ve ever known. My family treat him like a son because he’s just always been there with me since we were kids. Recently he made friends with a woman in his workplace and she turned up at a night out with the lads from work. They were chatting and she leaned in and kissed him, he had his hand on her leg just under her skirt on her thigh throughout the kiss and then apparently realised what he’d done and told her it could never happen again. I didn’t find out from him I had to find out myself when he got home on a second night out after this to find him drunk and passed out but his phone was constantly beeping with ***’s from another woman. From what I saw there were no images or sexual chat exchanged but he had been ringing her to come pick him up from the bar. I also found out they had given eachother lifts to and from work while sober. He swears to me that there was nothing other than that one kiss and that he regrets it and always will because he realises what he could lose. How the *** do I trust him again? He works with her still but she doesn’t come in his direction anymore because I am ashamed to say that I phoned her mobile and told her to stay away while threatening to go to their workplace and make their colleagues (our friends, her family and my dad) aware of what the two of them had been up to if she do much as breathed his direction! I’m so mad at him but I love him so much. We have three children together and have built a life together. He is definitely sorry, I can tell he means it but how do I get over him seeking attention from another woman? It’s left me feeling inadequate to say the least. Why am I not enough? He says I am but obviously I can’t be?