The onus is on both of them. The responsibility for a relationship is NEVER on one person alone. He is responsible for fixing this, but so is she. Even if fixing it is just talking about what they want and coming to the conclusion that they can't be together anymore.
Exactly. No healthy relationship can be one-sided when it comes to any level of falling out, and, at least to me, their relationship so far has been pretty healthy. They both bear the onus of fixing this. What remains to be seen is whether both of them will be willing to bear it. If either one decides not to work for this then the relationship was over when Angus left the coffee shop.
In a perfect world. Equal right, equal responsibility, everyone doing the right thing.
It's not a perfect world, even in the QCverse. If it were, this situation wouldn't have happened.
Angus has less of crippling burden, therefore greater resources. If he wants a continuing relationship with Faye, that means he--as the party with more resources--has to take on more work.
A healthy relationship is not what they have. If they want a healthy relationship, their options are A) The healthiest person carries the load until the other can should some of it. B) Both parties wait until both parties have equal carrying capacity.
B is a bad choice, something Marty and Dora realized.
In the real world, no relationship is equal. A truly healthy relationship is one where both partners have sufficient opportunity to play to their strengths. Each supports the other in turn, as life throws complications at them. Who is supporting who might change so fast neither knows who's hold who up. Or one partner might end up under the load for years.
Faye's damage is extensive. Angus's isn't. His options are to support Faye in getting better, or admit he can't do that. It's not fair, but neither is life.
Of course, that calculus may be moot. Marten was ready to shoulder that burden for Dora. Dora didn't allow it. Nothing says Faye is going to do give Angus the chance. After all, it isn't fair.