['My girlfriend is always worrying if I am as happy thought I would be after we decided to go from just good friends to be in a relationship with each other.  I always am honest and tell her the same thing.']
Sounds like she has some underlying issues with trust. You may want to sort it all out before you get too involved.
Last year my girlfriend asked me if I was ok with how life was turnig out for us. I stop and thought about how things use to be what we had hope for and how things are now, I looked at her smiled and replied I  I am .