I hear ya. I'm 31 and I'm still mourning over my first and last relationship that ended....4 years ago!!!!!
I've tried all kinds of things....matchmaking through friends (horrible), internet dating (weirdos), joined new classes and hobbies (nothing). Every failure reminds me of my ex and how happy we were and the "why things ended".
Every failure seems to me like an arrow pointing to the "you are going to live alone" statement.
Oh, for sure Ill also tell you the classic "well, you just gotta get out there and keep trying...." but seriously....doesn't this simply annoy you?
Good luck.