Casual sex with an introverted guy? Any perspectives?

Anonymous
A distant coworker of mine (different dept--I rarely see him at the office) has been showing interest on and off for several months. He's openly calls himself an introvert and is very serious about his priorities with his work and hobbies. Things took an interesting turn when we went out with a group of friends and were pretty drunk, went back to his place and had sex... for hours!

Despite this drunken fun, which I assumed was a one-night sorta thing based on his behavior, he invited me over two weeks later and this time we had a great night of sober fun, cuddling, stroking my face, and very affectionate behavior between all of the naughtier bits.

Still, he keeps very little contact with me and doesn't show interest in front of other people. I'm not sure whether he's actually interested in me beyond the fun we've had--though I'd sure like it to continue. I don't want to come off as needy, so I'm trying to avoid messaging or texting him too often. Any advice for next steps?
Casual sex with an introverted guy? Any perspectives?
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