Let me see ah....
Are you trying to say that your girlfriend had a relationship
before and in that r/s they were rather intimate. Even so, his body
language (ie walking in front of her) does not suggest that he
feels strongly for her?
If it's the scenario above, we cannot just assume from one
situation alone why he behaved that way. You are right to say that
there is something going on that he is not ready to acknowledge her
as his girlfriend. If he is much older than her, perhaps more than
10 years. Or maybe he is attached so did not want to be seen with
another person or it's his first relationship (but he did advance
quite far physically with her)..
what do you think? 
