This is a Public Service Announcement.
Don't date assholes. Seriously. Even if they're an asshole to everyone else except you. Even if you think they're kinda just like a rude comedian, but at least they make you laugh. Because guess what? One day, you're going to be on the other side of that fence. One day, you're going to be "everyone else". And man, is it going to be a doozy. You are not going to know what hit you.
Also, don't date Underdogs. Okay, that's not quite right...don't date Underdogs who blame everyone else for their problems. It's okay to be down on your luck sometimes and feel badly about it--but you pick yourself up and make things work. If you frequently hear things like, "The universe is against me", "I have the worst luck in the world" and "Everyone is out to get me", RUN. When you do terrible things in life, there are repercussions. When you have a nasty, negative attitude, you attract negative situations to you. When you look for the bad in everything, YOU. WILL. FIND. IT.
Don't be that sad-sack sympathetic girlfriend. Don't make excuses. Don't say things like, "He's a really good person...he's just had some shitty luck."
Because guess what? When the chips are down, he WILL screw you over without a seconds thought.
If someone does terrible things to other people, don't think for a moment that they won't do terrible things to you.
They WILL come back to haunt you.
And at the end of it all, and for years afterwards, you will shake your head in disbelief and ask yourself--was I really that blind? Did I really date someone who could possibly be so awful?
And you were that blind. And you did date him. Somehow, for some reason. Whether he had you thinking no one else would ever love you, whether you were afraid to be alone, whether you thought you could "fix" him...
And all you can do is move forward and try not to make the same mistakes again.
This has been a public service announcement.