Why would a girl get distant after sex?

A girl who I’ve been friends with at work, and got along with real good recently hooked up. It was great, we had so much fun, and after talked and really connected. Like it was the perfect day, because I have like her for years, we had sex, and talked like never before and I felt like it was almost too good to be true.

But the next day, we she walked into work, she just said hi, smiled and walked away. Like nothing happened. Some people said she has a boyfriend. But it was weird cause while walking by I tried to start a convo but she didn’t even stop. Is this normal behavior from a girl?

Why would a girl get distant after sex?
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