Welcome here, a good move ATM as you will, if you were like me, feel incomplete and hopeless.
There is no easy way I know of to get over the pain, except maybe anger. You have been ill-used. Maybe the person was immature and only starting to find out about themselves or if they were cynically using others.
There are two ways of looking at this - the loss and grief on the one hand -something inescapable - and the realization you have had a lucky escape
If he is thinking of who is more compatible with him then he is both selfish -thinking of himself first with no thought of others - and at the same time is on the wrong track. Compatibility is not the aim
So now you do not have to go though that selfishness and shallow thinking later on when you believed you were settled down together, it has happened early on
It is a learning matter, next time - and there will be a next time for you as there was for me - you will be looking for signs of true care
I talk of next time. It is so easy, particularly if it is a first serious affair, to think that's it, there will never be another - but that thinking will be wrong. It will sneak up on you as a surprise, it did for me, you will find yourself drawn to another and enjoying being with them. Then you find out if they are reliable and think of you.
Can I suggest that even if you do not feel like it, or are worried others will see the relationship is over and pass comments, that you do resume your social life. It will distract you and stop you being on your own -a bad thing.
It will let others know you are ready to go on with the rest of your life.
At the time I felt like not going on, taking my life the only thing as life hurt and seemed empty and hopeless. I'm so glad I did not.
My next relationship, with somebody who was so different from me nobody would say we were compatible, it lasted very many years till illness parted us
Do you have anyone you can talk to about how you feel? A family member perhaps or friend who will listen and care, not try to do anything to fix things -except go with you out for a coffee or something like that . Just be there for you?
If at times alone and feeling overwhemed or frightened of what you might do give either the Kids Help Line (1800 55 1800) or the Suicide Call Back Service (1300 659 467) a ring, or web chat if you find that easier. They are both caring, experienced and understanding. Just human contact can make a huge difference. (You may have to wait)