Just think that Im strong and even-tempered, please

I never want to show my weakness. Do you know that feel? But I found out it's not that good...
It seems like everyone believes I can handle everything. That they can tell me all their problems. But I can't endure everything neither! The result is, that when I have a problem, I dont tell it anyone - no, thats not true. I say it to many people, but I say it like "Hey, you wanna hear a joke? That boy I was dating with just broke up with me. No, it's OK, I knew it would not last a long time... I'm fine, really, thanks.". But when I'm alone, I'm crying for three hours, becouse I loved him. But nobody knows it and I know it's my fault, I haven't told it anyone. But I can't admit to let them know. They can't know that I'm broken and dragged down, that I'm depressed, sad and lonely. I should be the one who is fine and OK all the time!