<human>: Summarize the given text in a few sentences.

Relationship length : 1 year
Friendship length : 3 years

We had a great relationship (at least I thought so). He is the kind of guy who claims he's a natural flirt (should have been my red flag) and I was always arguing with him about that because to me, there is a difference in being friendly and actively flirting/leading girls on. But he talked well and always argued back and making me feel like the one who was wrong. I also caught him in many lies yet he still managed to talk his way out.

Then I found out from another girl(F/18) that he had been cheating on me with her. He apparently had a whole other secret relationship with her, telling her to keep it a secret from me and badmouthing me so she wouldnt ever talk to me. She didn't believe what he said about me, so she came to talk to me instead. We confronted him and he tried to lie his way out again. I showed him the proof I had and he came clean, but I had to prod and pry him out of all the details. Turns out it wasnt just one girl he had been cheating on me with.

This time, he was extremely sorry, kept begging for another chance and gave me all his email passwords, instant messaging passwords and allowed me to check on his computer/phone any time I wanted. He gave me a long, detailed explanation on why he did those things and wanted to seek professional help. After 2 weeks of thinking about it, I decided to give him a chance.

But now I resent him in everything he does. The things he says or does, I don't believe him one bit. He has not shown any sign of cheating, and he has stopped flirting with anyone, pretty much being a good person. I don't know how to break up with him now, or how to bring it up. On top of that, I also feel very vengeful, but I know it would be immature to exert revenge of any kind. But I also don't like feeling that he would get away without any consequence.
<bot>: Bf cheated on me with a number of girls, is extremely sorry, I gave him one chance. Now I'm vengeful and need help on how to break up with him without being immature about it.