1) No matter how much your girlfriend say's she loves you, a lot of times she will have no problem lying to you and screwing you over. Therefore, my advice would be to not take relationships to seriously until you are older, because if you do, you will get hurt.
2) No matter how honest a girl seems she is more then likely a liar.
3) Never date girls that have been diaignosed with chemical imbalances or depression/ and or bipolar. Girls like that can never be truely happy. They have a lot of ups and downs, they get mad and flip out over little things that normal people don't get mad about. Even when things seem good in the relationship, the girl could be uphappy. When the girl is unhappy she will seek the comfort of other men. Girls like this usually have self distructive personallites, meaning when things seem perfect, she will do something to totally ruin the relationship.
4) Once a cheater always a cheater. I've always believed that it takes a certain kind of person to be able to cheat on somebody and not feel bad about it. In my experience people like this never change. I understand that people get intoxicated and do things they normally woundn't do, and then feel terrible after they sober up. That isn't the kind of person that I'm talking about. People do stupid things when they are under the influence. I'm talking about the girls who cheat on there boyfriends while sober and never feel bad enough to stop cheating on them or tell them they cheated on them. Therefore, whenever dating someone new, always ask if they have cheated on a boyfriend. If they admitt to it, which a lot of times they will, don't start a relationship with them, no matter how much they say they will never cheat on a boyfriend again, or how bad they felt about it, they will always do it again when the situation presents itself.
5) The most important thing in a relationship is trust. Once that is broken there is nothing left. Futhermore, staying in a relationship where there isn't trust will drive you crazy, you will always be wondering what your girlfriend is doing and if she is being honest with you.
6) If you find out your girlfriend has lied to you about one thing, then it is very likely that she is also lieing to you about a lot of things.
7) Just because a girl goes to church, doesn't mean she is a good honest person. I'm a christian myself, and I have met way more girls who are honest, and have good morals outside of the church, then I have in the church. Many christian girls do bad things during the week, and then they think all will be forgiven on Sunday when they go to church.
Hopefully you will learn from my mistakes.