While it sucks, being pressured to marry has been a normal occurrence for lots of young men and young women, especially when they have a partner for long time. People don't care about their relationship's status, all they know and say is that "Oh you guys have been dating for so long. When will you get marry?" and follow by "when will you have kids, you should have kids soon", et cetera...
I assume the guy and the girl followed that normal tradition for straight couple as well. It was not occurred to them that they could just break up and find someone new despite their relationship having going dire because, well, what else to do when you are in such a long relationship? They were unknowingly pressured by the norms, and unknowingly chose to follow that norms which everyone expected them to do. It's honestly sad.