The night I stopped hearing from him, he saw me out with another guy getting food after work. The other guy and I have a strictly platonic relationship so I introduced them and even invited him to join us for dinner, but he just stormed off and I never heard from him after. Before this happened we spent a lot of time together and we always talked on the phone and texted each other, so obviously there was a mutual interest/attraction. He’s the one who didn’t want an exclusive relationship, so could seeing me with another guy make him feel embarrassed or jealous? Could he maybe have serious feelings for me but is avoiding me to protect himself? Is he suddenly not into me and I should just forget about anything romantic between us?
I just find it a bit strange because we’re all adults and whatever the case is he could just let me know. It’s especially awkward for me because I’m his supervisor so I have to maintain my professionalism and communicate with him whether he wants me to or not. Furthermore, I don’t think it’s appropriate for me to constantly ask him what’s wrong and try to get him to talk to me if it isn’t work related. So far I’ve been playing it cool and respecting his space by not going out of my way to communicate with him either, but from an outside perspective why would he seem so interested and then suddenly give me the coldest of cold shoulders?
This may or may not mean that he has feelings for you (which in turn may or may not mean he wants a relationship). People are often jealous even if they don't particularly like someone because everyone kind of likes the fantasy that they are the Greatest Thing Ever and learning that they might not be hurts. Also, even if he does have the feels for you, he may or may not want an exclusive relationship. (It's easy to like someone but also think you could 'do better' or just not to be up for the whole relationship thing.)
So what should you do? IDK. If *you* want a relationship, it might be worth calling him on it. ("Like, hey what's up with the cold shoulder?" and seeing what he has to say.)
With that said, if that doesn't get a long spiel of "Ugh, I hadn't realized my feelings for you until I saw this and now FEELZ!" I'd probably assume that, yeah, he's jealous and acting weird, but it's not great to get too wound up about someone who you've said you want more with and who has said he doesn't want a relationship.
You said, "I just find it a bit strange because we're all adults". Clearly, he's not an adult. Adults don't behave that way. Adults aren't afraid of real relationships, either. He was intetested as long as he got what he wanted without having to grow up. You're begging him to talk to you... to what end. He's emotionally unavailable, and his behavior tells you he has no desite to change that.
If you're looking for a relationship, he obviously isn't the guy for that. If you're just looking to resume benefits, there are apps for that. Either way, you deserve better than what this guy is capable of.