It sounds like you got involved with a fixer-upper. I could be really wrong here, but it does sound more like you were a personal trainer instead of a girlfriend. It's just kind of interesting that the only things you cite from the relationship was how you changed him. I dunno - perhaps I'm reading it wrong. But what you wrote left me feeling uncomfortable.
Anyway, when we make dramatic changes to our lives and outlook, our personality will also change. His world is now bigger and wider and he's a different man. If he's younger than, say 25, this will also account for a lot of growing and maturity on his part.
A sudden change usually requires a catalyst such as a different romantic interest, a change in job, a big fight etc. Or sometimes we can just have an epiphany about this person not being suited to us anymore.
What reason did he give for wanting a break? And what changes in his personality did you see in the last two weeks? You wrote that up until two weeks ago, it was perfect. Now, no relationship is perfect. They each have varying degrees of push and pull as we work out the big and small things in our lives. When you did disagree, were you always respectful to each other? Were each of you accepted by the other person's friends? Are your goals in life the same?
I hope you find the closure you're looking for.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.