Addicted to Love (1997) on Netflix

Plot summary

Sam works as an astronomer in a small town and lives with Linda, his childhood sweetheart and a school teacher. Linda leaves for New York City to take a two-month teaching fellowship, then writes to say she is staying. Sam heads for the city, sure he can bring her home, and learns she shares an apartment with Anton, a French restaurant owner. He breaks into a vacant building opposite Anton's home and rigs his astronomy equipment to watch the couple. Maggie, a photographer who rides a motorcycle and once was engaged to Anton, finds the operation and wants revenge on him, so she sets up her own room nearby. The two begin as adversaries and then work together to split Linda and Anton up.