After being with my girlfriend for almost 4 years now, I've cheated on her several times and don't feel bad at all.
That isn't right, why don't you feel bad about it?
I think it's just normal. When I'm with my girlfriend, I still think about other girls.
Cheating on your girlfriend is extremely selfish and the wrong thing to do. You are putting your own interests above the person who you are in a relationship with. You are wasting her time in this relationship and are going to hurt her when she finds out the truth.
She's going to be more upset if I tell her and she wants to break up than if I stay with her and keep cheating. Its normal to want to sleep with other girls.
If you truly feel like its normal then you need to be in a relationship with someone who can handle you having sexual relationships with other people, but you shouldn't just sneak around on your current girlfriend. Its unfair to cheat and she'll be hurt more when she eventually finds out on her own, you should consider her feelings and tell her what's going on.