Best way to get over a bad breakup?

My boyfriend of almost a year out of nowhere broke up with me, no warning or a reason. The day previous we where talking about getting promise rings... He's the first guy I've ever love so therefore my first heart break... They say things get better with time but I feel like it's just getting worse. I keep going through old messages trying to figure out what went wrong and It so draining but I can't stop my self... We've been through so much together and I just can't accept that it's over... Any advice on how to move on?