steve and bucky being devoted to each other above all else is not mutually exclusive with being intimate (sexually or otherwise) with other people and I think it makes sense for both of them to have (had) meaningful relationships with others that might veer into a not-strictly-platonic dynamic, through all stages of life.
and this kind of dynamic is typically spun as steve being undesirable on account of his disabled-ness, and thus the jilted housewife, while bucky verociously goes through every woman in brooklyn to play straight/temper his libido
or
steve post-serum being so overladen with sex offers or the love interest i dont care about, and realises that hey, I should spring the concept of a throuple on my traumatised boyfriend (worse: bucky graciously offers this instead)
and both of these options suck ass like first of all: it is massively insensitive in a boring way (steve and bucky are both massively insensitive in an interesting way). the first kind of narrative is always more so a reflection of what an able-bodied person would imagine their sexlife to be if they were to be(come) disabled. my opinion: sex and disability by mcruer is mandatory reading for everyone writing pre-serum stucky fic, exhibit a of the kind of sauce we should be giving steve:
as for bucky, who loves to be wined and dined and romanced and loved and fucked and desired and mused about - he unfortunately thinks that steve having sex with other people is a massive Big Deal, and bucky is something the complete fucking opposite of gracious, or forgiving. he's insane and it's not happening unless the other person is a) godtier special (a rarity, but still - there have been a few), b) also tries to get into bucky's pants ofcourse and, c) understands bucky's crazy (atleast a little bit, not asking for miracles). other way though? bucky is a hypocrite, he is (wants to be) very anais nin in delta of venus: "sex must be mixed with tears, laughter, words, promises, scenes, jealousy, envy, all the spices of fear, foreign travel, new faces, novels, stories, dreams, fantasies, music, dancing, opium, wine."
he wants to be worldly and have interesting sex and be cool and la vie bohème and get fucked in drag in front a crowd. and it's fantasy, but also not.
so he is always a bit on the verge of letting people compliment him too much. so he flirts a lot and not always harmless, is always inviting. but not sex. not without steve or his presence (steve only gives in those very few times so he can observe it with an artist's eye, so he can appreciate an extra set of hands, so he can inevitably fuck bucky better, so he can teach bucky a lesson and make him cry, so they can fight about it afterwards in their bed, cozied up).
but for steve, there's just some things he won't do with anyone that's not bucky. it's cause steve has only said "i love you" like three times his whole life. he says "youre great buck" "sweet baby" "thank you doll" and "end of the line" and he fucks bucky, that's how steve communicates love. sex doesn't have to mean love, but for steve it does. if steve is fucking you he loves you like crazy cause you're immensely, incredibly, insanely special and you understand bucky's crazy, and steve's weirdness, and you also want to get into bucky's pants and you're also just a good person and you should just be captain america. you'd be great at it, sam.
