Soorry for the long story.

I am currently living (relatively) hard times professionnally, which never happened before and is very difficult as studies and work always had been a source of ambition and fulfillement for me.

One of the few things that helps me get through this is a coworker from another department, who used to hang out with mine during breaks. We started to build a bond, we walked closely side by side apart from the group, talked of more private things. She is "atypically" attractive, always laughing and wearing this cute smile and clothes. I don't really like my job, but I like spending time with her, even more so that I am exhausted by the "main type" of coworkers I have. Of course, my dumb brain started to hope for more, as she never mentioned a partner to anyone, even if she likes to gossip.

She invited me to her birthday party, telling me that a very small number of people are invited, which I am very flattered by. I buy her a nice gift and apart from other few coworkers I vaguely know, is a guy I never met, a previous coworker. She just tells me his name and his job. I guess it's her boyfriend (verbal clues). The party continues, she keeps getting closer when talking with me, smiling more and laughing more as she gets drunk. She interacts sparsely with him, but he never really reacts a lot. He walks alone far in front of her. They know each other pretty well. The three of us come back together. She talks to me with her face awkwardly close (maybe two hands from mine), the other guy stays apart. She asks him to walk a bit more with her just in case and I offer her my gift. She likes it, hugs me, tells me it's cute... the other guy just looks from the side.

I am lost, is she in couple with him like I kind of heard or are they just close friends? My stupid feelings alter my judgments and I think about it too much, which makes me sad. How should I get things clear avoiding awkwardness?