I don't know what to do with my marriage

We've been married for about 2 and a half years. 6 months into our marriage, I caught my husband texting another woman. They would send each other pictures and flirt. It hurt me deeply, and when I brought it up to him he told me he would stop. When I was finally starting to trust him again, I logged onto his Facebook and found out he was flirting with his ex. Same thing happened, he apologized and it stopped..for a while. About 4 months ago, I noticed he would talk about a female co-worker more than usual, and would invite her to our house (I was always around so I knew nothing physical happened) at first, I thought it was innocent, she seemed nice. Until I noticed my husband would text her 24/7 and when I confronted him about it, he claimed he had no feelings for her but understood how their friendship would seem like it was more than just that. He stopped talking to her and about her unless it was just about work. Months after that, I kept letting every negative thing that has happened in our marriage get the best of me. Pretty soon, it was all I thought about and I became cold and bitter towards my husband. One morning everything got the best of me when we were talking about our past lovers and past experiences. I ended up bringing up everything he did wrong in our marriage and broke down crying about it. My husband consoled me and told me he had changed from all of that and was only focused on our marriage and confessed to me he did have feelings for his co-worker but stopped it when I started to notice. He says he would never have pursued it, he only flirted with women because our marriage wasn't "exciting" at the time. Even when things weren't exciting in our marriage, I never once looked elsewhere for excitement like he has. It hurts me deeply that these things happened and it makes me angry at him. Right now, I don't know what to do with my marriage. It seems like everytime I start to trust him again, something happens. I still love him and want to try and fix things between us, but I don't want his past mistakes to keep eating at me if we do try to fix our marriage. Any input from women that have gone through this would be much appreciated.