What did I do to deserve all this pain and regret? I can't take it anymore?

Long story short. Had a girlfriend for 2 years. We officially for good broke up because trust issues. She caught me messaging another girl and we were both a little flirty. Nothing sexual (I wouldn't have done anything, she was a friend). So she ended it because no trust. I'll be honest, we broke up a few times for different reasons. We're young. I'm 19 she's 17

she's had a thing going on with this one guy. Lets say his name was Josh. She sent josh nudes and I guess he led her on and used her and left her. I stupidly took her back. This was a few months ago. We were broke up at the time. I was NC for a month and she came back to me after he used her.

She showed little affection after we got back so I broke it off & went NC. She came back with a lot of attraction this time. She actually liked me again. Everything was great then she saw my phone and saw the flirty msgs.

I went NC for a week, & I hear she's been stressing about it & misses me so much. I reached out 2 days ago ago & she Denys me and says she Can't forgive me.. She's been talking to this brand new guy. Let's say named Alex. Alex was also in the picture during this 1 month NC a while ago I mentioned earlier. She sent Alex nudes too. Now they're back to talking and he's starting to lead her on. He made it clear that he's not looking for a relationship. Only to hang around.

this guy is starting to lead her on so he can get into her pants. Sad thing is that she's probably falling for it. I always tell her to respect herself but I guess she doesn't care. They've been texting everyday.

I stupidly bought her flowers for sweetest day & wrote a note. But then I found out this out & I've been thinking. Now I feel like she doesn't deserve them. Should I give it to her anywsys and just leave it from there? Just see what happens?

i feel like when I reached out to her to fix things, it was too early. Usually I wait until she eventually message me. She goes out and partied yesterday and last weekend with him.
What did I do to deserve all this pain and regret? I can't take it anymore?
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