Co-op randomly crashes

[[SqS] Wuag]

I bought a two-pack of this game and I have been loving it. But whenever me and my friend co-op I randomly crash whenever he hosts, and he gets horrible lag whenever I host. I just don't get it, the game runs completely fine when I'm playing single player, but in co-op I just randomly crash if I join a game.

[BRAINFOG]

where is your friend from? your connection speeds probably dont match??!