People can and do change their minds quickly. It's harsh. But it happens.
You should still be in your 'honeymoon period' of nice times dating and getting to know each other. But he's already telling you that he doesn't feel the same.
Possibly the relationship moved forward too quickly for him, given that he's not processed feelings from his previous relationship.
But even if that is the case I think you should hear what he's saying, and move on. Do you really want to deal with the angst of will he won't he change his mind? As he's unsure, better that it's happened 2 months in as opposed to 20 months.
Sorry you're feeling rejected.
I think as women we are pre-disposed to analyse the whys and wherefores of men and relationships. But sometimes there's just no rhyme or reason and even if there is a reason - whether he's just bored or fed up or feels hang on this is moving quickly not sure I want to be in a relationship right now - if the man is no longer interested then that truly is the bottom line.
He's already giving you the 'Its not you it's me' line just 2 months in. If you are going to continue with online dating, probably best not to put all your eggs in one basket quickly. You've not known each other long - are you sure he was exclusively dating you?
Why not just focus on yourself for a little while? Just getting your head in the right place, doing stuff you like just because it makes you feel good, hobbies etc, before going for online dating again. Or even getting out there and meeting people.
You have to try to build yourself up a bit because there are people out there who will come along and just knock you down. When you've invested your all, and they actually haven't. Widen your options, and just see what happens. You'll likely have to kiss a lot of frogs before you find your prince