Manuelle...

I am not really sure what you are asking in your post. Are you looking for some reason or rationale for your girlfriend's apparent drinking problem?

It is certainly highly suspicious that a grown man would spend time with a teenage girl in that way. Like you, I would be suspicious of his motives and if anything really did go on.

Does your girlfriend have any issues with intimacy that would lead you to believe that she has a history of abuse? Have you shared your concerns regarding her drinking with her? How does she function day to day? Is there reason to beelive that she is suppressing bad memories? Has she seen a therapists at all to see if any hidden memories could be flushed out?

My suggestion is to sit down with your girl friend and calmly talk to her about your concerns, especially her drinking. Do it in a very caring and loving way and do not be judgemental.