Why are things suddenly awkward between us?

ok so I like a guy in the same group of mates with me. we just recently became friends tho and things were going so well! he'd poke me and tease me and I'd laugh at all his jokes. we also started speaking online (he spoke to me the first time and I spoke to him first the day after) but then the day after I spoke to him, he kind of looked at me in a different way than he usually does. we barely spoke and he didn't joke around with me at all!

i'm not sure if it's because I spoke to him or that there's this girl he likes (who has a boyfriend) in the group and I happened to arrive next to them while her head was on his shoulder... kind of awkward really.
Why are things suddenly awkward between us?
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