This is the usual thing in Yaoi of "I like you and desire you so much that I can't help myself but take your body forcibly...". "Oh, no... yes... tears and excitation", cause' deep down his heart, Uke likes to be ravished. But aside the rosy and fucked up filter of BL, this is rape indeed... Because ML is hot, Uke is passive and thanks to BL... most will rapidly forget (if ever they knew) that this was actually forced sex.
The difference in size makes them look like they belong to 2 different species (one is a titan and the other human). I really like the art and how ML face is gorgeous, but the size difference bothers me as well greatly
The cause of these Yaois being like this is, as I understood, rooted in Japanese history, culture and fetishization, romantisization of rape/forced sex. This shows through their popular culture like anime, mangas (hentai, Yaoi, BL...).
Since Korean BL artists, authors, grew up reading these stories for many fucked up, we have this now...
If you want more explanations about this subject, I can tell you.
About the titan size, I believe it's the author's kink. In Secondo Piatto there was already this big size difference, and here it just got greater. If it's a kink, they may not want to correct it. But yes, the art is splendid. Coloring is also magnificient.

so just because of a "I missed you" we're supposed to look past the borderline r@pe?!
the physical size difference is also so uncomfortable and weird to look at... mc's whole body is the size of his one leg