GF was sexting with another guy, need some advices

I started dating my gf kinda abruptly. Specifically, I asked her to be my GF about 10 days after our 1st conversation and 1-2 dates.

She had male friends when we first started dating. I've always been doubtful about my parter having male friends, never been a fan of it. 1 month into dating, I found out that one of her male friends has gotten past normal friendship. I found out that he was an old talking stage, and they sexted and shared explicit photos about 4-5 times. 2 of those times were after we started dating.

She did draw a line with him and stopped sexting after about 3 weeks into our relationship, and I found out 1 week after she drew that line.

She was very apologetic, and has since then given me access to every piece of her electronic, the log-in of her Instagram, etc. and introduced me in person to all her families. She has also cut off every single male friend she had per my request. We have since then been pretty good, we traveled abroad during the summer. We are now 5 months into our relationship. Her families like me a lot, I love her very dearly and want to have her hand in marriage after she graduates college (2 years).

I'm still having such a hard time forgetting or forgiving what happened with the sexting. It would eat away at me and resurface every time we have issues. Am I too petty at this point, or should I have just left?