Because she has children and depression is treatable. When we make vows, we promise to love and care for our spouse in sickness and in health. I'm no stranger to PPD and have witnessed how difficult it is on a family. I do not have experience with a depressed husband though and my heart goes out to the OP. His reaction to her ending it is not one of apathy- he does care.
Yes depression is treatable. But a lot of people who have clinical depressions refuse to get the help that they need. At some point it because basically a choice on his part to abandon the relationship. Just because he is physically in the home does not mean that he is in the relationship.
There are more ways to carry out abandon a marriage than to walk out the door. Sitting there for years, angry, depressed, verbally attacking one's spouse is another form of abandoning the relationship.
I agree with separating until he demonstrates that he is getting treatment and that he can engage in the marriage and family. But I don't agree with throwing away the marriage entirely until he is given a chance to prove himself. A separation may be the wake-up call he needs to get help.
The OP said that he has
And I do know that running clubs/training have hurt marriages when the opposite sex is involved. I have no idea if that is what is going on here, but the OP said that she trains *mostly* with women. When your marriage is struggling, training with the OS where support and endorphins are involved can lead to bonding.
You do not know if the opposite sex folks in her running group are hurting her marriage. Does this mean that if a woman works with men, that she has to quit her job because there are men at her job? Are we now following Islamic rules that state that non-family member men and women must be separated?
I belong to a master gardener group that has both men and women. Does that mean that I need to quit the organization because there are men in it? Get real. Almost every one would have to quit because almost everyone is married... men and woman.
I also have a walking group and another special interest group that have both men and women. Do I need to quit those too?
In short, I understand that this situation is extremely difficult on the OP and anyone else who has gone through it. I do think she needs to do something here, as she can't live like this either. But I don't agree that she should give up on the marriage without giving it one last shot at shaking him up enough to get treatment and prove he can be there for her and the family.
She already gave him a last shot and he did not take it. How many last shots does she need to give him? How many years does she have to live in a situation that is not mentally healthy for her and for her children?