Hmmm more likely you may want to talk to your gf it isn't fair that your talking and thinking of someone else while your kissing, hugging her etc.
Because that's called cheating...
Put yourself in her position, wouldn't you like her to be honest with you.
Hiding things is also lying.
Just be careful dont hurt your gfs feelings
She sounds like a very nice person.
Think about it.
Good luck!!