How to tell if a shy introverted guy is in to you?

I have a coworker who I have known for 7 months. He is much younger then I am, and for the past few months it has been mentioned that he stares at me a lot. I have noticed it too. He doesn't look away when I catch him either. Sometimes I catch him doing what I am doing, if I am stretching so is he. Sometimes when I talk to him he seems really nervous and I can't tell if it's because he is shy and introverted or if it's because he likes me. I always make it a point to talk to him and after a while he lightens up. Sometimes when I leave early he tells me it makes him upset/sad. I will say are you sad that I am leaving and he says yeah, kinda. I don't know if he is looking for a friend here or a romance, but I wish he would tell me what's going on. I asked him a hypothetical question that didn't involve me and he stated he wouldn't date anyone he worked with. Maybe I am just nuts. Any advice would be appreciated.

How to tell if a shy introverted guy is in to you?
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