He is a cruel guy to just blurt it out and disappear, without further ado. He didn't tell you that even though he no longer loves you, he will always cherish the memories of your time together, etc. Either he is cruel, and then sour grapes, or he is simply immature. Maybe twenty years later he will tell you how important you were in his life. If he is immature, but about to get better, oh well and what a shame, but his maturation can take a decade and you cannot put your life on hold. Again, if he is cruel and insensitive, then sour grapes.

one approach is to collect all mementos of the relationship, put them in a box and store the box out of sight. Archive or delete all digital mementos.

another approach is to spend time grieving, listening to music he likes, looking at your pictures together, etc., until you feel you have done enough to move on.