You really think this part is not 100x more important than time elapase? If a man watching over a woman's every step in a do-or-die (I mean, D-I-E, getting annihilated by a mindless sentry bot, shot by a guard, erased from the living, etc.) situation is not a serious emotional catalyser, then... well, then we may be living in different universes.
First off, falling for someone begins with physical chemistry, which can be present between Zoe and Damien, and also between April and Cortez, but with Crow and Flipper - I wouldn't credit it that much.
Second, April did fell a bit for Cortez.
Third, none of April's mentioned relations has the visceral intensity of what I was trying to get across above.