Start with the pattern
Which Engine Is Decaying First?
Use what happens in an ordinary week to locate the first strain in closeness, effort or desire.
“Something feels off” can mean two different things to the people saying it. Look at what happens between the large arguments and the rare good evenings.
Bond
Do you avoid telling each other the truth because it will become a fight? Do apologies lead to a return, or does the room stay cold? If small bids for care no longer feel safe, start with repair and the way you handle conflict.
Effort
Who notices the next appointment, the empty cupboard, the child’s worry? Who has to ask before help appears? If one person’s invisible work keeps growing, move a real responsibility rather than promising to “help more.”
Desire
Do you still see each other outside jobs and chores? Can affection stay affectionate without an obligation to have sex? If the daily relationship has goodwill but no play or chosen attention, make room to meet again without a performance target.
If several are weak
There may be no clean first cause. Begin with the part that makes the others unsafe or impossible: coercion and fear require safety; ongoing contempt needs repair; overload needs a fairer load. Recheck what desire feels like after those conditions change.