Been cheated on.. What next?

After 7 years of marriage, going through ups and downs this past year has been the worst. At the point I thought things couldn't get better I made the choice to leave one day. I maade this choice bc after I was telling her how much I love her and how I want us to work she told me no, she's done, blah blah and she hates me. Hence, I left. Not less than a week later I received a long letter about how much she's loves/misses me, still imagines us growing old together, etc. I came back the next day. One night a couple weeks later I was looking for a phone number I lost by logging onto my Verizon account through old texts, in doing so I noticed a number she was texting back and forth with. It was the number of a girl she almost hooked up w in the past, I confronted her about it and her excuse was they were just talking about just little random things. I knew this wasn't the case and continued to snoop. However, after them texting for a few days it just stopped. There were no more logs of them talking.. Its now been three months. Then the other night I went to my sisters.. Once again I snooped and saw a text to her about how she found her hairtye in our bed.. Furious I confronted her, of course she lied through her teeth.. After hounding for the truth all day she confessed. I did find out however the night it happened was a night I was out with my sister and I didn't respond to her texts.. A few hrs of me not responding she got ahold of that girl. She says she will never do it again and I'd she feels like doing that again she will let me know so I can move on, but prefers to work it out and she's sorry, mostly for hurting me. Its clear it happened the one time based on evidence.. Idk it still cuts like a knife. Since the confession she's seemed in a daze. Advice please?