broke up a month and a half ago, news came to light yesterday, feeling horrible.

I just need to vent and maybe get some advice on how to feel better.

So, I (26m) was dating my now ex-gf (31f) for two years. We broke up over the phone, it was done by her, fine.

I found out two things yesterday that are making me feel like shit today. Basically in the third month of our relationship, she got drunk, some dude in a hot tub at a party (a party i was at with her) truth or dared her, her dare was to hold his dick in her mouth for as long as she could, her friends saw it, but she told her friends that we weren't official yet, so no one ever told me (her friends did not know me too well at the time).

Second is, she broke up with me because some dude who she has had a crush on for a long while expressed interest in her, so she broke up with me, fucked him, when she realized he only wanted to fuck her and leave her, she came crawling back and lied to everyone about everything that was going on making me out to be a bad guy for not taking her back.

This is eating away at me, not a lot, but enough because I spent so long with her, treating her so well and then...it's over and i find out this shit. ugh.

tl;dr - just found out yesterday that now ex-gf cheated on me way back at the start of our relationship and is trying to ruin my good name. how should i handle all of this?