What will he think when he sees me in a bikini?

my guy friend currently has a girlfriend, but he used to have a crush on me and vice versa, he's a flirt with every girl, except when his girlfriend is there, BUT with me it always goes further EVEN when his girlfriend is there, ex:(trying, lol I stopped him) to grind in front of his gf! I'm not sending him any messages that I'm interested so I know he's not misinterpreting anything, in fact I even told him who I like! My friends think its just physical, so does that mean I can't go to the beach or water park with him? don't get me wrong he's a great friend we confide in each other, like the same music, we do to each others events. If he sees me in a bathing suit, how would he react, since he's already grinding when I'm fully clothed:P?
What will he think when he sees me in a bikini?
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