Well, he used to. Now I feel that nothing can make me happy.
Unlike you, I don't think that not telling the truth makes things better. Your gf may be happier, but only b/c she doesn't know what is in your head.
If there is nothing wrong with it, why don't you tell her?
If that is alright, why would you hurt her feelings?
If you think that is normal, why would you make her insecure by telling her?
You KNOW that your gf will be hurt if she knew you are tempted by other women, so you decide not to tell her.
So, you are telling me that you are respecting your gf by keeping things from her?!
No offence, but that doesn't sound like much of respect to me. You don't think she can handle the truth, so you lie to her.