I NEEED HELPP:P plzz help me

Jim,
As you can see, I didn’t join the French Foreign Legion. I'd been up for three nights when I got that idea, so I was probably not thinking straight. I hope you got the postal order I sent you. Sorry, I know 15 quid is not enough to compensate for what I did, but I will send more soon as I can. Washing dishes does not pay well, you know.
I haven’t got a new house yet, but the gaffer lets me sleep in the back of the shed where he keeps spuds, carrots, and things, so I can keep the rats away. If you write back to me, send it to the CAFF on here. I'd be very happy if you'd write back to me. Every day, I think about what I did, and I'm ever so sorry, Jim. I remember my fifth birthday; you walked me to school and said to the big / older boys, ”here's my best friend; he's five and his name's Gavin”. Do you remember that, Jim?
I wish I could remember doing those things I did. I'm so sorry Jim. Maybe you'll come and see me one day? I hope so. Got to go now, time's is running out. I'll write (more) soon even if you don’t. Tell Sally I hope she gets better.
From your friend
Gavin

 what did he do to Jim? What is he apologizing for? I don't understand it:S

I need some help...plzz help me