one foot forward...
That's alright fella, tbh I don't have any special insight into how things work. Maybe I've just had a bit longer to think about it
It will be hard, but for your own sake, no matter how much it hurts (and it will, which is ok), you have to start thinking about
you as you are now, today. Forget about where you have already been, you cannot change that.
The sooner you start thinking of 'me', I' instead of 'us, we' the better.
Change
up some part of your life so it's totally different from what you used to be with your ex. Get down they gym, take up a pastime that is new to you, anything, so long as it takes you in some new direction. The worst thing is to remain in one place, figuratively speaking, with nothing but old stimuli undermining your sense of self and purpose.
It's not going to alter who you are over night, but as a process you will turn something painful into a part of your life you can look back on and not be overwhelmed by it.
Who knows, through that 'new thing' you've discovered you might get to meet new people and do a whole bunch of new things you might never have had a chance to experience before. And in time, when you look back on it, you will realise you are a better person for it.