I think that throughout their entire journey sam is like "im sure mr frodo cares for me, he tells me as much, but I don't think he loves me in quite the way that I do for him...oh well, that doesnt matter. all that matters is that I help him because I love him, even if he never loves me the same in return."
and then once the ring is destroyed and the two of them are recovering in gondor, suddenly all the love and affection that frodo had been withholding comes out all at once and hes constantly hanging off sams arm or stealing kisses or leading him away to quiet and private areas to be alone. cos from Sam's pov hes like "guess mr frodo's just not that into me." but frodo's pov is "theres no point making my attraction to sam known since I am going to die in this journey anyway. its not fair to him to show my romantic intent when im doomed and I will likely be the reason he dies too. all I can do is tell him how grateful I am for him"
and once frodo DOESNT die he's like "oh. well. we are boyfriends now"
