Blindsided and Completely Heartbroken

My wife is leaving me and it doesn’t make sense. We have a 5 yr old daughter together, we’ve been through tougher times, I just recently got a great paying job and lost a bunch of weight…. Things were thriving for me and she tells me she isn’t in love with me anymore. I can’t imagine a life without my girls, a life without my wife, her with someone else, or a different father figure in my daughter’s life… I’ve never felt so sad in my life. I assumed there was someone else just because it would make sense, but she swears there isn’t. I’m every emotion possible and I’m losing my mind. Can someone please explain how I can possibly move on? Where do I start?