I'm going to tell small lies to my girlfriend.
Why do you want to tell your girlfriend small lies?
I'll tell any lie that makes my girlfriend happy.
It is normal not to want to make your girlfriend unhappy but you shouldn't achieve that by lying to her. It will make her feel betrayed when she finds out the truth and lead to the end of your relationship.
A few little lies aren't such big deal.
If you lie to make your girlfriend happy you may find that she is very unhappy that you deceived her. This could really hurt your relationship, I think you should be honest with her.