Hi Mystiah. Thank you for sharing your story. I think you'll find many people on here are willing to read your posts and offer what advice, support they can.
I am sorry to say this but I am seeing red flags.
I think what alter ego posted was right on the money as far as commenting to your friend that he is a great kid brother. However, I don't get the impression that you or your friend view this relationship as brotherly/sisterly. Instead, I get the impression you are head-over-heels in love with this young man. And he with you. Am I correct? If this is in fact the case, I think this fact trumps everything else and I don't think you can offer much help until you clear this part up. I think you really need to tread lightly in this situation. In many states and across the world, your friend is still legally a minor until the age of 18 and it concerns me on a number of levels to read about your situation.
Since you are the adult in the relationship, it is up to you to set the tone. You need to make it clear, in no uncertain terms, that this is a platonic relationship and your feelings for him are as a friend- nothing more. You are at an age where you are most likely looking forward to stability, marriage and children. Your friend is in a completely different stage of life. He is most likely looking forward to prom, graduation, and college. (maybe not so much if he is suffering from SA but, you get my point) I know you've said he is very mature for his age but he has yet to experience life out in the world. It seems to me you are most likely getting abuse from him because he is still, in many ways, a child. And a child who is feeling rejected will often lash out, having not the maturity nor the resources to draw upon to act any other way. Over all, your relationship raises quite a few questions, at least for me. Why would an intelligent woman 25 yrs of age turn to a young 16 yr. old boy for emotional support? Do other people know the full extent of your friendship with the young man? What do his parents think? Do his parents know the extent of which the two of you talk? What do your parents think?
Also, I think people all too often compartmentalize their world. Using terms such as "real life" this or that. There is only one life and it is all real. Online or otherwise. Often times, especially for someone suffering with SA, the online part of life can feel like all there is.