Work crush

I am very confused by somebody who I work with abd would like peoples opinions. I have known this guy fir a couple of years, was close but drifted for a while when we worked in different departments, we are now back working together and getting close again. We are very playful and flirty (we hace water fights in work, he wipes his hands on me after he has washed them, if walking together we shove into each other, he never waves just screws his face in a funny way). We have very jokey conversations, can also be very dirty, never really anything serious. When he sends me an email there is always 2 x's on the end of them, though i do not do it back (I am aware this may be habit). A friend has pointed out that he is a little feminine sometimes but from what I have told her he likes to act manly with me. A few work colleagues who have guessed i like him say there is a spark and that we would make a good couple (I think they are saying it because they know how i feel, not because they think it is how he feels). We have never seen each other outside of work and do not share mutual friends, I know he is very reserved which is stopping me from taking things further and I can't read his intentions. The other day he mentioned the fact he finds a woman attractive in work but stopped himself saying anything more and said "I don't know why I'm discussing this with you," as i have said we are quite close so why would he feel he cannot discuss that with me. Also, (not sure if it is just me) but i get the feeling i am being watched sometimes, when i look up he is the one in my eyeline and he looks away from me quick. I really don't know what to make of it and it is doing my head-in, as I have said he is reserved and the fact we work closely with each other makes it awkward to say anything out right to him. If anybody can offer any advice, good or bad, please heelllppp =(