A common trope I rather dislike is the trope of the disappearing significant other.
The idea is that a couple is dating. They are still figuring out their feelings. Then, one member disappears on a business trip or into a work project or to another country or to visit parents. Sometimes, the significant other announces the event beforehand but quite often, the vanishing act is unexpected. The first member, the one who was less sure, realizes, "Oh my gosh, I really do love this person!"
The trope isn't entirely useless. It shows up in Cherry Magic between Tsuge and Minato. However, in that case, it is truly more of a plot point than a crisis. The crisis in the relationship comes later when Tsuge confesses that he can read minds (and Minato reacts far more normally than Kurosawa did to the same revelation from Adachi--though Kurosawa's reaction is hilarious).
What is less believable or bearable is when the vanishing act is used to force feelings I'm not entirely sure a character feels. In Real-Time Fever, Shizuka goes home to tend to his father. Kurosaki, who is something of a playboy, is forced to confront that he wants a full-time relationship with Shizuka--.
Sure, when people don't get what they want, they can get quite possessive. It's one reason that auctions and eBay are so effective for sellers. It's one reason that car dealers say things like, "Oh, it will be gone tomorrow." Desperation, a feeling that one is going to lose out, a sudden flooding of "I want" emotion can swamped the rational part of the brain.
What happens when the significant other does comes home? For that matter, what happens when the relationship moves from high emotion to everyday life?
In truth, in reality, absence can break or almost break a relationship--as Only the Ring Finger Knows demonstrates. The heart doesn't get fonder. It gets more self-protective.