Hot and cold friend what would u do?

I have a male friend (im a gal)but i find him hot n cold. Hes a little bit of a loner and tends to befriend alot of girls but hasnt really got any friend friends outside the office. Anyway i made friends with him since aug. We got talking and he asked me to lunch so i returned the favour. He nagged me to go over his new flat so i did. I email him now and again but he doesnt seem to be good at initating just at the replying and seems he doesnt give alot out of himself. He says im open person but i wouldnt say the same bout him. Hell go to lunch with me when i ask and does little things like appologise to me if he dont reply to my mails and theres always that flirty banter yet he dont make much effort his side. Hes worksworthy so i take that into account. He can be moody yet will get jealous ifi ask someone else to teach me to play snooker. I wish he would make more effort his side my instinct says he likes me