Everyone feels off balance in the first months and even year after the BD. It's normal because you have no indication that they are doing to tell you that it's over, they don't love you like they use to etc. However, his journey began 18-24 months prior to BD and he had a head start on shutting down his feelings/emotions for you and the relationship. He's moved ahead w/his feelings/emotions while you are just now floundering. But, at some point, he may feel the way you are now and you will have moved forward w/your life. But, that will be many months from now, even possibly a few years.
As for the ow, please try not to give her any head space because she is taking up space and not paying rent. She's nothing more than a good time, Band-Aid and as I've mentioned to others a FXXk buddy. The so called love their are experiencing is nothing more than lust and having a good time. It is not what we consider a deep, emotional love. Think of it as a young kid having a crush on a little girl in the class. It's not real love.
There is no rhyme or reason for some of their comments or actions because the crisis is based on depression and yes, it's an emotional journey for them. They go back to the time where they were stunted emotionally and have to face their demons, accept what they can or can't change and hopefully grow up and become mature adults. Some make it and others don't. Those that don't, remain lost.
Keep the focus on you and your daughter. Any word on your grandfather?
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.