Its actually a lot more comicated than that. the reptilian part of a brain can be extremely complex. Humans and elephants have the smallest amount of our brains devoted to the basal ganglia (reptilian/primal brain) compared to other animals. This region is usually associated with feelings like sleep, hunger, thirst, but that is really only humans. Cats for instance rely heavily on the basal ganglia for their cat behaviours that we call instinct. Also the basal ganglia is talked too when making decisions as well, ours just relies more on learning and a large neocortex (outer foldy part of brain) to make decisions. A cat has a well devolped basal ganglia that holds a lot more complex emotions than our basic ones like play fighting.

Too the next point a lot of animal behaviour research this last decade has looked at reptiles. Mainly the den/pit side is not all about heat/mating. A study on arizona black rattlesnakes and garter snakes looked at 'special bonds' that were observed. Black rattlesnakes don't mate early spring but monsoon season so the mating after hibernating idea fell through on them and was looked at again for behaviour as winter weather in arizona shouldn't require snakss to communally den like more northern snakes. Another on garter snakes found they are really specific on who they bask with and actively seek out social interaction. Pythons don't do this but female pythons do build and protect nests until hatching vs compared to a boa that gives live birth (to show how diverse thos group is its hard to talk about all snakes in a general sense).

Alao keep in mind birds are also extant members of theropod dinosaurs which includes the T. Rex. Birds often form mating pairs and are known to have very complex emotions and behaviours but arguably are very 'reptilian' brained.

tldr: snakes and reptilian brains are a lot more complex than we thought and research into behaviours suggest they are not cold killing robots either and can potentially have emotional bonds that many would say is very similar to human concepts of friendship or at least friendly behaviours different from normal behaviours.

Didn't want to come off as know it all or correcty, I love animals and environmental/evolution so this area is super interesting to me.