What is the best way to get over a breakup?

i was with a guy for only 7 months, and we had a great relationship, we were even going to get married and have kids someday, but then when i was unable to contact him his sister let me know that he was moving to be with his ex, now i can't get over him, i have dreams about him almost every night and they are all the same dream, me stopping him from going to be with her. Let me know what is the best way to get over him