FWIW, the largest I've played is 10/20. I don't play online. I consider myself usually TAG. When the table/situation warrants, I loosen a little. I don't know all the numbers and don't consider myself an expert, but I rarely walk away with less than I walked in with. Having said that...

I was with you until your 3-bet on the Flop. I wouldn't have done that. But, you did and MP is still riding along (chasing?) and CO just called? So, maybe you're still ahead.

I definitely would have checked on the Turn. But you didn't and MP's still hanging in and CO either feels he's got you (and MP) or that he can run you off, so he raises. Now you figure you're in deepest doo-doo and bail out. At this point I think I'd have seen the River.

Your question was about learning how to fold. Hell, how can you learn to muck A-J? Who teaches that? Like I said, the only thing I'd have done different was that Flop raise.

Maybe somebody's got a lot of good reasons for you not to have played the hand. I'm anxious to see how the hand played. (inquiring minds and all that)