im just feeling that he is being cohorts into things he knows nothing of and have explained to him that it seems to me that he is being lead by the nose as he has learning problems and is naïve but the problem is he is 18 and classed as an adult
You mention 'learning problems' are you your son's appointee, do you have any involvement with other agencies, or does he have complete control over all his affairs because he has capacity?
I understand that you feel he is being coerced into this new exploration of sexuality, but the more you show opposition to it, the more likely he is to want to defy you.
That's a combination of his hormones and possibly emotional immaturity. Often people with learning difficulties can present with an emotional age about two thirds of their chronological age and that makes them very vulnerable to exploitation by their age peers and others.
Telling him he's vulnerable and easily led isn't going to help, he doesn't want to hear the 'you're different' talk, he already knows he's different, that's why he's experimenting and trying desperately to fit in.
Your actions really depend on your son's circumstances and if not handled very delicately, it could drive a real wedge between you. You want to protect him, that's only natural, every mother would, but you have to tread carefully not to alienate him, because he won't see your actions as trying to help him, he'll see them as controlling and interfering.
Does he know about safe sex (at the very least to use a condom) and does he know about consent?
The cup of tea consent video is very good and explains things really well, can you watch it together although you may have to reinforce the message about the metaphor.
www.youtube.com/watch?
v=pZwvrxVavnQ