one sandesh for you, you are just 21. Its an age of getting attracted. And given that we live in a society were we try to repress our sexuality as hard as we can, getting attracted to anyone closest to us or even shows a little affection towards us is very common. But, its just temporary and try not to mistakenly take it as a permanent thing. Give yourself some time. And if it helps try to think about the hottest or most prettiest unmarried girl around you, in your class may be, or even a hot actress while masturbating.
Your aunt is affectionate because she is a women, and take it from me women are genuinely caring to everyone around them. Its their nature so don't get any wrong idea. And as much as thinking about it does not make you a weirdo but acting on it will get you in a serious trouble. So don't even think about touching her.
You want some strong advice, try to avoid her for few weeks or atleast keep safe distance and keep your hands to yourself. I hope you will be successful to control your urges.