I learned this one the hard way.

I should have done this. It would've saved me from the heartbreak.

That's kind of what I did. A few years ago I fell for a girl hard, the first girl I actually ever loved. Then a while after we started dating one of her old "friends" came back and she eventually broke up with me for him. It was awful. Then a month after that she admitted she had feelings for me still and I still did too, of course, but she didn't know whether or not to stay with him or choose me. I told her to just stay with the other guy. She chose me. And a month later we broke up because it just wasn't working. Stuff happens for a reason.

This could have saved me the pain a few months ago. Well, I know it for the next time.

No, dont leave them.. immediately. Its hard to pick between a person you love and a person who is important to you, leave themmto make the desision, dont make it for them.