You need a crash course in detachment. You have to start now and start hard.
I know that the last year went well, but if it was so good, how come she sought out other men? These things don't happen "accidentally" unless you are in the proper mindset.
This, and what she is saying now about giving you time, makes me think that your perceptions might be quite different. You might have seen really connecting, but I wonder if what she saw was a man that was bending over backwards to kiss butt. A man that made a complete reversal from being harsh to completely the opposite...basically a butt kisser. NO RELATIONSHIP is without some strife...and you had one for a year and I can only imagine it's because of how you changed your behavior. She may have doubted it was a new you. She may even have felt like it was a quite superficial way of keeping her. Sure, she probably liked it, and went along; it was nice having you so docile and eager to please. Perhaps you could have used some of that time in your own pursuits rather than just devoting it solely to her. I suggest that you do so now.
Start today on establishing your own identity as a guy that is capable of having his own interesting life. Do the things that are suggested to newbies...get a hobby, get some independence, get a life. She gave you the heads up that she's wanted out for 14 months now. Show her that you've accepted that and quit wasting so much of your time on her. There is no reason that she should get upset of you moving forward since that's why she didn't leave before...because she was so worried for you.
You cannot be lonely if you like the person you're alone with. Dr. Wayne Dyer