One challenge is cultural differences. For example, different holidays and how to celebrate them. Another is family acceptance. Families may have certain expectations that the couple has to face.
Not at all. My Dress Up Darling manga is far from being cancelled. It continues to attract a large fan base and the creators are actively working on new chapters.
One interesting story is a school dance where the name tags got mixed up. Boys had girl's name tags and girls had boy's name tags. It led to some really fun and unexpected dance partners and a lot of laughter.