When you fall for someone, you fall for them, and no amount of rational reasoning and stacking up reasons why it's bad for you will stop that feeling.
So ending that relationship - as opposed to having it ended for you, is a massive step to take, and it will need a lot of time for your to assimilate the new circumstances into your life.
People talk about 'getting over' a breakup, but I don't believe you do get over it, I believe you weave it into the fabric of your life, and eventually it finds a place there where it doesn't cause you massive pain on a daily basis.
That takes time. The cliche 'Time is a great healer' is like all cliches - true. But no-one mentiones that 'time' is not a short measure, so you need to accept that, it helps towards the process of getting on with your life without this man in it.
At first, it will be a constant presence, always there, always hurting. But because the human psyche is good at healing itself, that massive hurt will receede, but it can come roaring back without warning. Don't look to feel better a bit day by day, that's not how it works. It can come back ages into the future, brought on by a sound, a thought, a place, a smell, any of those things can suddenly plunge you back into your grief as though it was yesterday.
But again, thos incidents do pass, so you simply have to allow the time taken, and try to be good to yourself.
The hardest part is not going back, because that will simply scratch open the wounds that split you up in the first place, so you ned to be very very strong, and know that you have done the right thing for everyone, however agonising that feels in the small hours.
You will get past this - there is plenty of support on here, so post away, there are good people wo will be there for you when you need them.
A x