Getting mixed signals from a guy

I need advice from people that maybe experienced a similar situation or if they can recognize the signs of some behaviour, because honestly this is turning me into an obsessive person.
So, at the start of this year I started a new job. This is my first real job as a professional rather than bars/malls/etc. For the first month, I was extremely depressed. I have bp disorder and I had recently been having a LOT of "low" periods with very few "high" periods in between due to a very stressful family life as regards money/education. I would lay in bed until 7pm on my days off, get up, eat a day's worth of food, then sleep again. I couldn't focus in work, and everyday was a battle to stay awake at the PC, despite me getting about 18 hours of sleep every day on weekends. I started hearing things too each time before I would begin to lose consciousness, like a rush of sound or dishes falling...
About a month into my job, a bunch of new people started. It was very strange; I'm not very sociable, but I was able to speak to most of them no problem when we passed each other in the halls, but there was one guy and something entirely different happened.
Now, disclaimer, I have NEVER been in a relationship with anyone. I have NEVER been kissed, by girls or boys, and as such I don't really consider myself to fall into a specific category of sexuality. I say "gay for simplicity" because right now, the thought of being with another male is appealing to me.
Anyway, what followed was 3 months of extremely awkward eye contacts, head nods, and bashful look-aways whenever I caught him staring. I even began to keep track of it in a diary just because I had no idea what was happening and why this guy kept staring at me, or why I found him turned around looking at me whenever I looked up from my work (I sat behind him, so he had to turn to look at me). I thought nothing was going to happen; it was harmless staring. Towards the end of the 3rd month I decided to try dig up some info on him. From his social media I found out he was gay, but not only that; he was living in my apartment block. My depression subsided rapidly, finding myself always energized, waking up earlier than necessary, even choosing to walk the long way to work. All because of these little interactions.

A few days later in work, I heard someone behind me while I was looking at my PC, and suddenly it was him. I won't go into details because it could give away my identity, but he basically said he found out I lived in his building and had "no idea" (which I find doubtful for similar reasons I can't tell).
That night I decided to add him on social media since we were a little more familiar. Within 10 minutes I was in his room, revealing my life story. He questioned my sexuality, and honestly, he's the first person I've ever completely opened up to. I felt so comfortable and you would think I was lying if I told you the amount of times we finished each other's sentences, or just totally freaked out in agreement over so many things. He is quite attractive, I'm attractive too, but not "classically" like he is, but during those hours I felt like he could look like anything and I would still adore him.

Although he didn't mention it, I found out through my access to his social media that he has a boyfriend, and least from his last post less than a month ago.
Do you think this is fair of him? Maybe I'm the one being unfair, digging too much into something that I shouldn't just because I have a particularly hard crush...all I know is that if I had a boyfriend/girlfriend I might think twice about inviting another person to my room after midnight, or engaging in very overtly sexual talk with them, or blatantly checking them out for 3 months straight, then proceeding to make ambiguous private messages to you.
He seems happy in his relationship from what I can gather...is this fair to his partner even? Please, this my first experience of liking someone, and I'm just peeved that it HAD to be complicated. I haven't eaten since that night, I simply can't, even a few pieces of candy makes me stuffed, and the other night I shocked myself when I burst out in tears for the first time in over 10 years, and I was laughing because of how ridiculous it was to just suddenly start crying!

I've considered confessing, or manipulating the conversation to a point where I can confess, with no expectation of reciprocation of course, just for my own peace of mind...

Thank you!

 

Thanks for your comment! Unfortunately, things moved EXTREMELY fast after I posted the thread...long story short, we slept together...beforehand we had a very frank conversation about his relationship...He said he loves his bf, but was unsatisfied with things he had done in the past...
I'm not really OK with just being that other guy, but to be honest, I have never been more happy during those few hours than ever before. Now I'm sad though, because I don't know if I could ever trust being in a real relationship with him if he breaks up with his bf.

 

Thanks man I've always found comfort in online peeps (gamer kid).
I moved country with this new job, so everyone I know is back home, A LONG ways away. I don't really have anyone as a result ^^ I keep myself sane by keeping a diary...not just about this, but other issues I've had. I really don't want to get depressed again, it's so horrible being so lethargic.
I think I'll make a followup thread...