Why did he pull away after sex?

This guy and I are coworkers. We have known each other for a year, and we have been great friends. Recently we started talking and flirting. We hung out on the weekends and finally had sex. Now, suddenly he acts like i don't exist. He stopped texting me unless i text him first and even at work he does not acknowledge me anymore. Please dont just say he used me for sex because it leaves me so puzzled, as to how he could have acted sooooo interested in me and suddenly he is cold.

We hung out every weekend and yesterday i asked him to hang out and he told me no withoug saying 'no'. Im so sad and heartbroken as i really felt like he cared for me. Now i feel like i lost him and its driving me crazy. How do i grab his attention again?
Why did he pull away after sex?
Add Opinion