Crush on a co-worker

How do you know if a co-worker has a crush on you or is at least attracted to you? I have this coworker whom I’ve encountered due to an employee engagement thing that went on for weeks. Then from there we started becoming friends. The vibe was really evident. He usually messages me randomly about our common interests. Like almost everyday. The only problem is that he has a girlfriend. So my interaction with him is kinda limited and I don’t usually initiate. But can’t deny that it’s really fun when we get to hang out. I’m kind of curious if he is somehow drawn to me like even just a crush, or he is just really friendly. For you guys who are in a relationship, do you usually message a coworker (you just basically met but vibed really well) randomly about random things? Or what do you think?