Love / How to read the signals from this Polish Guy? [19]

I have a polish guy colleague and my other coworkers notice him that he always look at me, happier when I am in the vicinity and more gentle towards me. I just dont mind it as I haven't notice it and dont give malice on it. But when we discuss about professional things, he really do segue and always put topics like inviting for a dinner with candle lights. However, I always reject his offer. As far as I want is to separate professional and personal life. He even text me in a little naughty way (suggesting intimacy). As I answer that it is not that easy. I even say that I feel awkward about the personal messages he give. And he reply that if I am bothered he will stop immediately. He really do stop. We only do have exchange of messages about work and he dont do a personal manefestation of inviting dinner and whatsoever. He invited ones of playing a sport we both love (as always been used to by the office). I thought that he invited the usual people playing so I said that I am on it.But its only me and the other close colleague of him.

Also When we meet in the office, I start to observe him now that he is staring at me, being gentle of me (when he is known to be a hard and rough head), he explains when he cant reply immediately.

I am starting to develop feelings toward him but I doubt if he really do have interest to me or just wanted a hook up. And I am afraid to entertain my feelings or do entertain him since he will be ending his mission in our country and will be assigned to another country.

What should I do?:( Now, I wanted to know him more but I have already rejected alot of his invitation and he stop on relating to me on a personal tone.

In addition, How to spot if a polish guy likes you and you are not only assuming?