Listen to Cadet here. He is right. Her unhappiness isn't your doing. Not by the story you've told us here anyway. But one thing, and this is related to my current sitch. Friends? Seriously? She sees you as friends? Do friends really treat each other like this? Mine don't, that's for sure.
My ExW is trying desperately to friend zone me right now. It's not going to work. Don't get me wrong. I'm not being a jerk, but I'd rather be fired as a husband than demoted to a friend.
Her story as you've told it doesn't pass the smell test mate. Seriously, have you noticed any other out of the ordinary behaviour? New hair cut? New underwear? Slimming? Hitting the gym? Staying out later? Anything like that? I really hope there is no OM involved but I could change your sig to mine and it would be just about right. Sorry man but that what I see here.
Me:43 Her:42 M:14 S:9 EA started 2014/03 (or there abouts) PA started 2014/05/30 BD:2014/11/05 I left 2015/10/01 I returned 2015/05/02 She left 2015/06/10 OM still on the go.