Yeah.
First girl I was with for 2 years, she cheated, got back with her for another 5 months before she broke up with me - as well as telling me she'd cheated again.
Proceeds to tell me she wanted to be single for a while before getting with a guy she met on a job centre course less than a week later. Ironically this was not the same guy she'd cheated with.
I would not be surprised if she had cheated a 3rd time with the guy she got with tbf.
Long story short, that time was a ****ing disaster and probably put me on emotional lockdown for 3months because during that period of my life I was a beta af mess. Wouldn't be surprised if that's was why she did it tbqh.
Second one was pretty recent, with her 8 months in total, probably about halfway through we split up and it took around 2 months before we got back together. It was alright but this relationship was always really volatile and apparently people felt it was toxic and were surprised we'd lasted 3, especially considering the second half of the relationship I was actually at uni and we were doing an LDR.
Without wanting to sound like too much of an ******* I'd argue that most of the problems and drama in this one were down to her being of questionable stability and her friends being a bunch of thunder*****, though. There were at least two guys trying to convince her to cheat, for example.
Realistically it was probably a lot of strain on her with all the other stuff she went through and I don't know if either of us were really ready to "settle down" so to speak.
Tl;dr: twice and neither went too well.
As a side note the first girl is still the only one I've had sex with. This was entirely my choice as I've had offers for casual sex/fwb and just never went far enough. Right now I'm at a point in my life where I'd honestly have good pizza and some peace of mind than emotional investment and sexual positions, ty. I might regret this decisionmaking in a couple of years though when I no longer get any attention.