Well, we can guess but only she can tell you why she's unhappy. Work on communicating with her.
It's always a little tricky, but you've been together a year, it's OK to confess some feelings when asking what's going on. Maybe something like "You know I think you are sexy and I love you but I feel kind of worried lately and I want to ask, Are we OK? You can tell me to stop being silly

" Then sit back and listen... don't keep prying if she's dismissive.
Unhappiness is always the root of the problem. Not that she's interested in another guy, or that she needs time apart.. Unhappiness, her loss of interest, causes those things to happen, not the other way around.
Once you figure out what's going on, that will help, you'll be relieved, then start trying things to build up attraction.