Sleeping with 14 year old son, appropiate or not?

[a_few_queries]

Hello, I just have a question pertaining to my GF and her 14 year old son. She has been a single Mom for half of her son's life and then got married when the boy was at age seven (Her ex-husband was not his biological father). Obviously she has now gotten a divorce and we met early on in her seperation from her ex-husband (alittle over a year ago). I have noticed that on occassion her 14 year old boy sleeps with her whenever I'm not there (I work nights four days out of a week) and recently - in the last week or two - this behavior has somewhat increased. He has slept with her probably three or four nights that I haven't been there over that time frame. I feel uncomfortable with that situation occurring, mainly because of the child's age but also because neither one of them (especially my GF) seem uncomfortable with it. Furthering more background to this is the fact that the boy is more sexualized for his age then some other kids that I know in his age group. Also in her previous relationship with her ex-husband, the boy would try and sleep together with them and be forced by the ex-husband to sleep on the floor in their bedroom, right up until the boy was roughly 12-13 years old, when finally he slept in his own room. Finally, my GF did confide in me that one night last summer, he did enter her (our) room and tried to "imitate" me while she was sleeping - talking in a low voice, calling her by her name rather than as just "Mom" and some other things that I did find disturbing. I feel that I'm not over-reacting to this and I haven't brought it up with her yet, but feel that maybe alittle honest feedback would help me before I decide on what my next action should or shouldn't be.

[Haddock_Entrap_Propulasion]

I really don't think there's anything inappropriate going on there...given the ex-husband forcing him to sleep on the floor (or at least not with them), it may b that sleeping with her constitutes some form of reassurance and...kind of anti-rejection?  (I'm sure there's a word for that that I don't remember).  
Regarding what happened last summer, if he feels comfortable enough with her to sleep in the same bed, he may also have felt that she was a safe person on whom to "try out" that kind of behavior, especially if he thought she was asleep.  I agree that that's a little creepy, but it seems more like a sign of immaturity in some areas than of anything bad going on.  
I wouldn't advise doing anything just yet...keep in mind that he's 14, an age at which people change very rapidly, and the process of differentiating from the parents begins.    It's very possible that he will decide he doesn't want to sleep with her anymore sometime in the near future.  Unless something changes in such a way as to make you concerned, I'd say leave it alone for now...if it's still going on by th time he turns 15, then you can start worrying, although the problem there is more one of a probable lag in emotional development than of anything inappropriate per se.