Yeah I was with a girl for 5 years, 3 of them being engaged and she started falling for this guy as well. I sure as hell didn’t get it – fully unattractive – but when I found out I said, “Are you F****ING serious? I’m out.” I ripped off the ring she’d given me, tossed it at her (although I wanted to whip it) and left… I looked back a whole lot, but I left her. 6 months later I met my, now, wife. Been married for a year now and I wouldn’t give that broad the time of day.
Furthermore, if she’s willing to break up a marriage, what makes you think she’s going to stick around with you if you two decide to get married? I know that a big reason me and my ex were together for so long was because we’d been together for so long. We both felt like if we ended it we’d look at it as wasted time, so we stayed together and hated each other. Asinine. Don’t look at it as wasted time. Look at it as learning what you DON’T want in a woman. Sit there and make a list of her flaws. Don’t list anything nice. But for your own good, just leave her. You’re not gonna do yourself any good by staying with her.