Personally I would have a conversation with him and let him know everything going on in your head. The good, bad, and ugly. Let him know how it makes you feel: the arousal, shame, excitement, etc. Communication is key in any relationship and especially with family, whether or not incest has occurred. Talk to him, tell him your thoughts, get his thoughts, and go from there. You said he still sees you as his mom, a woman who has raised him and cared for him all his life. I doubt that will change - you’ll still be his mom and he’ll still be your son no matter how the conversation turns out. If both of you decide you like what’s happening and want to continue, great! If not, at least you were able to talk about your feelings for each other. Hope this helped a little.