Well I love to think that Kyle and Cartman are super sweet to each other while they're alone other than that I think that mainly Eric is the one being romantic but as soon as anyone else is with them they act like rivals again ripping and insulting each other mainly Kyle being the one to really lay into him getting so pissed that he might even beat him up but at the end of the day he with give him bandaids and help him but be really grumpy about it.