Listen, every guy thinks, "What if I never get laid again.." after he breaks up with/moves on from his last girl. I've literally thought it dozens and dozens of times. Guess what, you always find someone new.
And you're not miserable because of some twenty-four year old mother of three. You dodged four speeding bullets, my friend.
You're miserable because people at your age are miserable. You're figuring out life. You're transition from living life as a kid, where you have zero concerns, to a life as an adult where everything sort of sucks.
The best thing you can do is find a few things that you like. Games, traveling, concerts, pounding one-night stands--whatever, and really enjoy those things. Because in reality, you're going to spend 80% of your waking life working. And then you'll die.
Cheers, mate!