As a budding learning game designer, here's my issue with it: I've always defined immersion as how closely the feelings of your protagonist/avatar and the player are aligned.
Character: Oh no! Goblins!
Player: Oh no! Goblins!
Character: Grrr, you stinky sorcerer!
Player: Grrr, you stinky sorcerer!
Character: I'm ready to take on anything!
Player: Why the hell aren't there any health potions here??
That last part would be an immersion break.
That said, forcing the player to "love" another character, or even give the option, strikes many as a bit creepy. They're a mess of polygons with a voice actor/actress. Besides, many of us (myself excluded) have significant others, and what the hell would you say to them while playing that game?
So I don't blame most developers for excluding that sort of thing. It's dangerous territory in the feelings of many players. HOWEVER, I do see one way it can sort of work. Basically, avoiding any emotional attachment of your own character, and having various romances occur among the support characters can have its impact, especially if you helpfully get involved in some way (rescuing a man's wife from a dragon and bringing her home to him, to watch them hug each other and thank you endlessly). Additionally, I played a game called Digital: A Love Story, in which the reciprocated feelings of your own character were never said, or even implied; the girl you meet just kind of admits she developed feelings for you, and calamity prevents a fully-formed reply. Having not expected anything of the protagonist, that one worked well.
It's a pretty tricky subject, overall. It's not the same way as you'd develop a romance in a movie.