Empty on the inside is spot on. A couple of months before BD, my Xbf's younger sister had her first baby, a lovely little girl. Let's just say he was less than thrilled at the idea, and at the hospital he was barely interested in looking at her.
I remember so clearly when we walked out and I asked him: "So, now that she's here, how do you feel? Are you happy?"
And he just kind of pulled a face and said "I guess I haven't realized it yet."
....NOT NORMAL.
Also on the phone, when he called me to announce it was over, I was being friendly, asked him about the new apartment he furnished, he gave me lots of details and then I said, very breezy: "That's good, I'm glad. You must be happy, right?"
And he was just kind of silent and mumbling. Didn't sound like it.
I don't remember much from my depression 6 years ago, but really, the way it seemed impossible to ever feel happy again... man. That was horrible. It all seemed so hopeless.