Questions: Guy's Behavior

I have been noticing this guy around work. He works in a different department to me and sometimes when we made eye contact, he would smile and hold his gaze. I would always be the first one to break eye contact. I eventually said hi to him and after that, he ignored me and avoided looking at me, like actually turning his head in the opposite direction.

Recently, he has started saying hi to me (he is the first one to say it) and I plucked up the courage to have a proper conversation with him, where I introduced myself.

The whole time, he had a big smile on his face and was fidgeting and moving closer towards me. He asked where I work and I told him which department and what time I finish. He said twice that he would have to come and check out my area.

The same day, my colleagues said they saw him walking past our office (10 mins after I left) and glaring into the office the whole time. And I’ve never seen him near our office.

Today, we said hi twice and the second time, he gave me a big smile when he saw me. When I was sat down in the canteen, I could see his reflection in the window and it looked like he was looking at me/in my direction.