Guy's Behavior

GUYS HELP! My brothers friend and I have sexual tension? He flirts but has a girlfriend?

he knows that i find him really attractive our mutual friend told him (embarrassing) anyways so he knows i think his hot but this past few months I've noticed a change in the way he looks at me. He came up to my holiday house and we went to the beach together and other friends. He kept looking at me like only when my brother wasn't around.. then on the beach he was like joking around asking me if i had i had a boyfriend and i was like being a little flirty "its boyfriendS plural" and he was like laugh smiling, i ignored him so i just continued on my phone ignoring him and he like grabbed my phone and was like "who are you texting?" and i hit him! and he stood beside me like towering over me saying "what are you going to do im bigger than you" ahah i got it back and then i lied on the lounge he followed me and like stroked my legs to feel how soft? I DID NOT ASK HIM. whenever my brother was around nothing!. i saw him again last night we were watching sports in a dark room with a projector. i wasn't sitting near him but i through my peripherals he was looking at me and id turn and he would move. Anyways again he touched my leg when i went over to sit there near him and again he took my phone !!! So then we were just chatting like normal and i said " its my 18th in July " and he stood there shocked looking at me for a minute and said "you know im only a year older than you " im not sure if he's being nice or flirty? am i not the little sister anymore"? what does it all mean?
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I REALLY NEED SOME GUY ADVICE
GUYS HELP! My brothers friend and I have sexual tension? He flirts but has a girlfriend?
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