WherecanIhide, essentially inthat conversation you had he told you that what you found and how you felt about it was not of any consequence, and managed to shift the focus onto him and some problem he feels he may have, with the implication being that it is him, how he feels, what he is going to do about all of this, that matters and you can wait around until he makes up his mind to stay or go.
One of the big issues here is that he feels you and your feelings don't count, therefore. It's all about him. Yes, that can signify depression, but it can also be a habit.
I would give him a week to find somewhere else to stay, be it a hotel or whatever, with a view to finding somewhere permanent -- this might have the effect of making him focus on the fact that you are a living breathing human being and not some wifey-shaped figure who has clearly become just part of the wallpaper in his life. You need to make your presence felt here. Force the issue.
Please get a hold of his laptop and phone too -- after all, if you hadn't found what you found, when would the possible question of depression and the midlife blahs have come up? How much longer would you have been living with a man with impotence and all that that entails? Apparently, until you found what you found, he was bumbling along fine, not wildly happy maybe, but not willing to face himself (and the impact on you remains unfaced). Only now when you have told him what you know, has he come out with some explanation (again no reference to your hurt). Keep probing.