My nephew hits on me?

I think you are correct in being concerned that he must have an attraction to you. I think a talk is in order that you are his guardian and really wants him to enjoy as many people, especially girls his age as possible. Now if he comes on to you, you have a decision to make. Personally, I would turn him down but then again, it all depends upon what you fell for him and how much you really want to get involved.
Remember, once you cross over, there is no going back.

Teenagers have a natural sexual curiosity. The hormones raging, and so many new emotions and physical feelings to explore. So if you feel that this goes beyond just normal curiosity, then you might need to have a talk with him.

But you should also consider that his family was killed. The love and affection he shows you sounds like he's trying to fill a void that the death of his parents left. You sound well-rounded, intelligent, and caring. There will be some attraction from him because of that. You should also consider that if he knows you are gay, he feels more comfortable around you to act more like himself. If he is gay, do you think you are a good role model? Kids (even teenagers) often mimic what they see. In your case, is he watching you work out to get turned on, or watching you work out to learn how to do it for himself?

There is also a 9 year difference between you, and although written 9 years sounds like a large difference, in actuality it isn't that great. Probably some shared interest in Music, TV, and other things like that. He might feel close enough with you that he wants you to teach him how sex works. Maybe it is curiosity, maybe it is a type of love. You need to think about your own limits, and set them. Sort of like, you'd do anything for him so you want him to learn safe practices, but at the same time you don't want to cross that border and turn it into romance either.

Find out what he wants. The only way you can do that, is by talking to him and getting to the bottom of it. Be open minded, don't judge, and don't react negatively. Those would hurt him, and he's already hurting. (Example: he comes out sand says he wants you to be his first. instead of freaking out and saying no and eww, just say its something you'd have to think about, but until then you ask that he respect your privacy)

Don't you have a lock on your bathroom door? I think you need to tell him to knock before going into people's bedrooms. I'd say don't confront him about this unless he starts full on flirting, but don't encourage him e.g. working out in front of him, walking around not wearing much.

Hopefully this is will pass. Good luck.

As a teenager, I had such an odd sex drive. As I grew up, it changed. Still weird, but it has calmed down, especially since I've had a steady partner for a few years. Lock your bedroom and bathroom doors when you need privacy, and maybe ask him why he doesn't bring anyone home. From there, talk about his sexuality and then encourage him to date people from his school. Even just for experience. Or avoid the talking and stick to hoping he'll grow up quickly.

As someone who is also attracted to an older relative, I think this is normal. Even if it's not, I don't see anything wrong with it. You should talk to him about it, but don't make him feel bad about it. If you can accept it, you should be accommodating to his desires. As long as you aren't pressuring him into anything, I think it's healthy for a boy to explore his sexuality with someone they feel safe with, especially someone with more experience. You clearly make him feel very safe and happy, and now sexual. Life can be difficult and complicated. Don't make it more repressive and complicated for him than it as to be. Let him explore and decide for himself what he wants.