How to deal with coworker?

So, I have a coworker who presses basically all the buttons for what I find attractive in a guy. Intelligent, fit, nerdy, funny, kinda shy like me. I'd ask him out, but I'm not sure if he's gay or not and I'm not sure what, if any, tells I should look for.I've been at this job just over a year now, and the position expires end of January. He was the first coworker to come up and talk to me during work and invite me to lunch, as well as basically the guy who showed me around the office, and I basically wound up helping him organize our website.In that year, though, he's been single the entire time. As far as I know, he's only had one date during that time, and it didn't go anywhere, nor do I know if the person they went on a date with is a guy or a girl. I've tried facebook stalking, but I haven't seen photos that I think would necessarily qualify as photos of a girlfriend as opposed to a girl who's a friend, and he clearly doesn't keep it updated much. He's also dared me, and only me, (no other coworkers to my knowledge, who are all female with the exception of our boss), constantly with the silliest dares during our lunch breaks, stuff like "How much would I have to pay you for you to dab after ordering your food"? He's even paid for my lunch a couple times and even a beer (though that one was because I had done a dare).But most recently, when our boss managed to hook the entire office up with suite tickets to a basketball game, we had to pose for photos a couple times. Both times, he stood to my left and had his hand in the small of my back. One of my other coworkers noticed this and joked that "No wonder you guys didn't bring plus ones, you were each others' "! Afterwards I noticed that he changed his seat so it was the one next to mine in the suite.And I'm not sure how to deal with all this. I don't know if it's just wishful thinking on my part and I'm misreading benign things, or if he's actually hinting, or if it's just harmless coincidence. If I knew for sure he was gay, I'd ask him out without hesitation. At the same time, I don't want to waste time on a fruitless effort or get my hopes up (however hard that may be).