Hi I Have A18 Year Old Son That Lives With

hi i have a18 year old son that lives with me. i can see delayed memory function ,with delayed answers to questions ask, at time you talk to him,he's next to you and he does t even focused on what was ask. he would laugh by himself, smile by himself. always wants to be alone or would go for a quick walk and come back. his lips are always moving as if he is talking but not saying award,always gazing in space and looks serious. i recently noticed that he would go in the bathroom for a long time . Can you please help.