Would you leave your boyfriend/girlfriend if you found they were on a dating site?

If we had established we were an exclusive item then yep. I would move on. What's the point of being with someone that's clearly looking for someone else? So you can be their temporary chick/ guy while they scope out dating sites for the next best thing? He/ she isn't trying to make friends, it's a DATING SITE for a reason. So I'd drop them and move on. People that have the ability to tell a lie with a straight face, will always use it.

Absolutely I would dump them, yes.

Someone on a dating site is looking to date, which means if I hadn't been cheated on yet, it was only a matter of time.

If they are looking for someone else, they clearly don't want to be with me, so the relationship is over, one way or another. Might as well make that official.

If they are flirting with other people behind your back, it's break-up time.

A person who stoops to such a level is not trustworthy. When in a relationship, two people are to remain exclusive to each other. Flirting is the pre-cursor to cheating.

caught her on a dating site = not interested in ''me'' = leave her...as simple as that.

nothing i trust her --- i have to question if i am really an important part of her life and if im not then its good bye ---- there are actually many people on dating sites looking for friendship and not romance

I would so mad at them I mean that means they aren't committed to your relationship and are probably trying to see other people or it could be just them trying to have fun messing with people online so dont be to mad