1 : Let people make their own decisions without interfering. People fuck up, so be it. That's life. 2 : These types of feelings are normal, but acting on them isn't usually a good thing unless you know someone is in real danger. Now you look like more of a dick than the guy you tried to separate her from. Learn from this, control your jealous feelings from now on. Try to surround yourself with people who will help you understand when you're doing something wrong, that's what real friends do. Don't kick yourself down and just move on from this, you're too young to be hung up on one woman like this. Take your lessons learned and apply them the next time you feel this way.