A broken relationship
"A broken relationship can make you feel more lonely than when you were single."
Experience is the best teacher but the thing is...it can also be the worst. Ask anybody who has been dumped before and their story will move you to pity them. The worst kind of loneliness is experience when your relationship hit the rocks. You seem to give up on life and if left unattended, depression sets in.
I'm going to tell you that it's not the end of the world. Get up and get going. You are not the only one who is passing through it but you may be the only one sulking about it. There is more to life than just sitting in one place and mourning your situation.
Don't give up just yet cause you can meet that special someone that God has destined for you. You can be happy again if you choose to be.