Husband confessed

Hi all! So my husband and I have been married for three years. A couple months before we got married I caught him texting a coworker. I read the texts and they seemed flirty and I told him he was starting to cross a line. He said he would stop talking with her and as I was only his second real relationship I just thought it was innocent and trusted him. One night before we got married he stayed out until 4am after supposedly going to the gym. He said he fell asleep in his car. I’m so naive but I believed him! Fast forward three years. We have a son, we have a great relationship but I’ve always mentally gone back to that night. I’ve kind of always known and I’ve been living with it in the back of my mind for these past years. I finally confronted him about it and he admitted to having a relationship with her. They would close together at work and make out in his car. He promises no sex or sexual things happen but I just don’t believe that since he’s been telling me false stories for three years! I feel like our vows are all a sham. That our marriage is fake. My whole world and what I thought was whole and wonderful is all just one big lie. I feel broken and empty and have nobody to talk to about it. He cried so hard and he can’t explain why he did it. He promises that it stopped before we got married but how Can I trust him? I have thoughts of running away and leaving him and thoughts of trying to work it out. Counseling? I need help. I’m mentally unstable right now and don’t know what to do. We ended up crying together and hugging but I don’t feel like I can move past this easily. Has anybody been through this?