I think that this behaviour is problematic and that family counseling is in order! He's too old for this behavior and if you plan on taking this relationship further, it could present huge problems down the line! Honestly, the mother should really put a stop to it IMHO!
Prayers are with you...
I think this behavior is worrisome. I have a 15 year old son and can't imagine him coming into bed with me and saying "Let's make out." I would truly be horrified if he did, and immediately get him into counseling- after booting his butt back to his room where he belongs. Has your gf considered putting an end to this, telling her son to sleep in his own bed because he is a young man now? I don't think you are overreacting- I think that this poor boy sounds quite troubled and his mom needs some parenting counseling to help her figure out the issues that are going on. She also sounds like she may have trouble either "letting go" of her no-longer-litttle boy or maybe it's that she has trouble putting her foot down with her son and setting limits. It's hard to say no to kids, but it needs to be done, otherwise they never learn how to act.
When you mention that the boy seems overly sexualized for his age, do you mean that he is sexually active? Or that he simply talks a lot about sex and comes on to girls a lot? This could be way off base, but I wonder if he's ever been sexually abused. It just sounds like he has sexual behavior mixed up with regular parent/child affection. I say goodnight to my son most nights, and he will ask me to scratch his back or rub his feet or shoulders- but there is a very clear line of what kind of physical interaction he tolerates from me. Anything too cuddly, even though I obviously have only pure intentions, is met with "Eww, Mom, stop!" Hugs are to be brief and kisses are discouraged- there is NO chance of cuddling in bed. This is because he has experienced sexual attraction/contact with girls and the thought of interacting in any similar way with Mom makes him sick. From what I know of teenage boys, this is pretty typical. Some are more affectionate, some less- but I think you are absolutely correct to think something is "off" with how your gf's son relates to her- and how she allows him to relate to her. This is a precarious situation, but I don't think it will get much better if left alone. It seems like this boy wants to replace you when you're not there, and I'm wondering how he feels inside when you are there, even if he acts OK. Some hostility is normal from teenagers when their mom dates, but this sounds more like him wanting to BE you than drive you off.
I think that JoJo is right- bring up the idea of counseling for all of you in the most tactful way possible. You don't really need to tell your gf that this is the reason you want counseling- she may become defensive. You could just say that you really want this to work well and for everyone to adjust happily, and you think you could benefit for some group counseling with them to be sure you become a supportive, positive figure in your gf's son's life. I admire you for taking this on- I hope everything works out for you all.
I don't see anything wrong with his behavior. I have a 21, 18, and and 13 year old and they all slept with me all the time, since my husband is always gone at night at work. They would fight over, who was going to sleep with mom. They always hugged and kissed me all the time. They still do even though the 2 older ones are out of the house they still come over from time to time and still sleep with me. Maybe your girlfriends son was making fun of you by acting like you. He might not like you for some reason. Maybe he fills like every guy that comes into his mothers life is going to end up hurting her,and he wants her to fill like hes always there for her all the time. At the same time he needs to fill that his mom stll needs him. That's just his comfort zone, he just fills safe sleeping with his mother.
I think you should ask for some family counseling to take place if you are planning on getting married. You should phrase it that since there is an ex-husband in the picture and a young man that would be your stepson that you would like to make sure there would not be any problems between all of you. Maybe you have some other issues that you could use as an excuse also. Usually a seperate meeting will take place for each of you where you could bring up the subject and see if it is considered normal.
I can understand an occasional time of being upset or hurt and needing some comfort but this seems not to be the case here.
I am a grandmother of a soon to be 15 year old and this doesn't seem like normal behavior to me especially since he is already involved with girls.
When our kid's are dealing with issues that our world throws at them on a daily basis I believe it does not hurt to share a bed with your teenage son. If all parties involved are aware of the reason for the support. When my 15 yr old son is troubled which is what we are facing at the moment he is having school problems and is on may police charges, he is confused and needs that parent/adult support at the troubling time, we often chat on my bed then he does go to his own room but he knows he is welcome if he needs to be with me and do not find this behaviour inappropriate. If my son needs me I will be there 24/7 as all we parents do.
You do make some valid points and I understand that he may feel threatened by me and my relationship with his mother (as she has stated to me frequently that her son does recognize how much we are in love with one another). Yet he has never shown too much of an outward sign of aggressivenss or anger towards me and has gotten less so as time has passed. Saying that, I have to admit that I wasn't totally forthcoming in giving all the details of what happened last summer - in that some of the other "disturbing behavior" he did also included asking her to "let's make out." His mother does have a tendency of being half asleep/half awake and not always cognizant of what's going on around her in this state - he would obviously be aware of what she is like under these circumstances as well. And while I respect that he maybe "trying out" some kind of behavior - as you have stated - he has no issue with getting girlfriends and isn't shy with them either and I would like to keep in mind that he was - as his mother stated - seemingly trying to imitate me when doing this.