This is based on personal experience of dating for several years and a few long term relationships.
Have initial promise and a long lasting spark: Duality, Activity, Semi-Duality, Mirage, Benefit
Has initial spark but difficulties follow:
can't help each other, too much of same: Mirror (better for friendship, many times I've seen mirrors make the best of friends)
stagnation: Quasi-Identity
subtle opposition and discreditation: Contrary
can't rely on them: you as Supervisor
get the life drained out of you: you as Supervisee
No spark, steady as it goes: Business, Identity
No spark, can't be yourself around them: Kindred
Too different to understand each other: Superego, Conflict