im gonna steal some headcanons from myself that I posted on tumblr a while back. these are some numbknee Deep Cuts (tm)
- cartman is THE most doting boyfriend on earth, period. like once he and kyle get together, he is OBNOXIOUSLY affectionate. ridiculous pet names, outlandish PDA, copious romantic gifts, you name it. he puts his whole dang pussy into showing kyle (and the world) how much he loves him, and kyle (secretly loves) HATES it
- kyle on the other hand is very much a "show don't tell" kind of person, with his main love languages being quality time and physical touch (with the latter preferred 90% of the time in private hence the annoyance with PDA. he does get caught up in it sometimes tho when cartman eggs him on and finds himself in angry public make-out sessions more often than he’d like to admit)
- after they get together kyle still calls cartman by his surname out of habit, but he slowly eases into calling him eric in private and eventually does it the time (but still calls him ‘cartman’ when he’s particularly pissed off lol)
- cartman LOVES it when kyle lets him do his hair if they’re going out to a party or something. kyle’s decent enough at styling it himself but he gets lazy/annoyed with it sometimes, plus cartman’s got that special artistic touch that really makes his curls POPPIN
- cartman is a shameless pillow princess but can also be surprisingly giving in bed (esp because he gets off on getting reactions out of kyle and making him squirm). for example cartman is like.... scarily good at giving head
- kyle is surprised when he realizes how much he enjoys post-coital cuddling/doing aftercare shit and often gets more fulfillment out of that than the actual sex part. cartman of course also LOVES being doted upon
- this one might be a bit obvious but cartman can dirty talk as easily as breathing. it kinda puts kyle off at first cuz he doesn’t have a clue how to do it back until he realizes dirty talk doesn’t have to be that corny ridiculous bs you hear in porn all the time. he keeps it honest and doesn’t force it, so what comes out of his mouth is pure, straight-from-the-id horniness and cartman eats that shit up like candy 
- if/when they get married, cartman gives him the cheesiest fuckin vows ever but they’re so stupid and genuine and loving that it makes kyle angry-happy-cry on the altar and they end up fucking in the bathroom immediately after the ceremony’s over lolololol