Broken hearted

So my boyfriend and I of almost a year broke up a like two months ago and I’m still sad. In a way it was an extremely toxic relationship I ended but it was a very mutual break up. But for some reason I’m still extremely sad and all I do is miss him. He’s already been with two or three chick and it just hurts to know he moved on that fast. Plus we both lost our virginity to each other so I just don’t understand. So sometimes I get really sad and think to myself that he was the best guy I’ll ever get and it just really puts me down in the dumps. How do I get over him?