I fucked my best friend?

Ok so I ended up in bed with my best friend! I have known him for 15 years (mind you I'm 21) and we were laying on his bed like always and he just came out of the blue and kissed me... I didn't stop anything and we needed up sleeping together.. I still talk to him like nothing and I notice he's changing asking me out get more protective I don't know just acting more like boyfriend without being my boyfriend if that makes sense. and I don't know what to do I don't want to ruin our friendship if we talk about it and want different things... Any advice?
I fucked my best friend?
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