You have good cause to be concerned about this. Young people with Aspergers and High Functioning Autism have a lot of difficulty recognizing when someone is lying to them, using them for their own purposes, or befriending them in order to get them involved in inappropriate activities. Many “Aspies” are surprised that someone would even try to take advantage of them. While they understand if something is true or false, they can’t understand why someone would use the truth to create lies, say one thing but mean something else, or believe something that is not true.
The slow or confused processing of emotions many people with Aspergers experience can impede awareness of dangerous situations and stop rational thought. The emotional warning signs that are meant to protect them from difficult or harmful situations may malfunction, or work so slowly that they lose effectiveness. This means that these individuals are less prepared to defend themselves verbally or physically in an argument or conflict or say “no” to inappropriate activities. Consequently, your adult child may fall victim to exploitation or worse through no fault of his own.
Even though he is a grown-up, you must still try to protect your (socially naïve) child as he is not ready for the same amount of freedom as other grown-ups. Does he have a trustworthy friend or relative who could be a mentor and help him by going out with him and keeping him out of trouble? This mentor can try to help your son understand that many people act friendly, but may want to get him involved in foolish or dangerous activities. Also, the mentor could help him get involved in clubs or groups in which he will meet responsible friends.
Therapy is definitely called for in this situation. You and a therapist may be able to convince your adult child to tell you what is going on when he is outside the home. Also, he needs to tell you when “friends” want him to do something wrong or dangerous. Convince him that by doing so, he is doing the right thing, obeying the law, and keeping himself and others safe.
Sit down with your adult child and have a long talk about what he shouldn’t do when he is with friends, including inappropriate sexual activity, criminal activity, take drugs, drinking, driving after drinking, and so on. Make it very clear to him the negative consequences of doing each of these things in very specific terms. Make it clear that he must not engage in these activities – even to gain the friendship of others.
One of the good things about young adults with Aspergers in this situation is that they can be very “black and white” in sticking to rules. So, if you can emphasize some of the laws around certain behaviors (e.g., petty crime, certain sexual behaviors, use of alcohol/drugs, etc.), you have a much better chance of compliance. In such situations, quite rigid thinking can be a good thing if it helps to keep your adult child on the “straight and narrow.”
Also, consider the possibility of a temporary group home or an assisted living situation for your son to help him learn to become independent and act responsibly, thus preparing him for living on his own some day. In addition, it's probably a good idea to put your name on all his bank accounts so that both of you must agree before he can access his money.