besides the well-known fact that tony stark's arc reactor literally powered his heart and symbolised his second chance at life, it's been not just alluded to but clearly stated by marvel from the very first iron man film that it represents his heart:
this point is made very clear again when it's used to portray his death:
of course they did this; they're such obvious metaphors that are easy to rely on for beautiful visual storytelling. they undoubtedly were aware of the potential for these scenes and carefully considered them since the beginning.
but you don't really get to use each of these moments more than once if you want them to matter, so they had to choose which one of tony's stories needed to be told through carefully picked parallels.
and who did they use them on?
yup, that's right. steve rogers. steve, who literally ends their painful fight by breaking his heart.
steve, whom tony literally hands his heart and says "here, take this" while he's devastated, disappointed, and at one of the lowest moments of his entire life.
so, platonic, romantic, alterous — the intricacies of his feelings don't even matter. they're only for tony to know.
but what we as an audience know, what we were explicitly told by marvel, is that the feelings tony had for steve were so strong that they were the equivalent of getting his heart actually shattered into pieces, and being reduced to offering your desperate, mourning heart on a platter as a way of saying "take it all, there's nothing left of me that you don't own now".
these were not accidents. we were meant to understand how profound his feelings were. so many things spiraled out of their falling out — the entire universe's faith was at stake as a result. tony was not indifferent to him. his problem was that he felt too much.
tony's achille's heel was always steve rogers, and that will forever be the backbone of the marvel universe.
