Oh, for goodness sake, it's all hard.
But for me? One, just the sheer length of time. And the not knowing when it will end. And two, having to hear about his "wonderful life". He sends the kids texts or e-mails saying how cool things are where he is on holiday and stuff like that. So that's also the "conspicuously leaving me out" of this new life. Watching him be "fun Dad", while I get all the hard parts.
And the 'twilight zone' feeling that we really are on different planets, that this just isn't my H. It's hard to believe that the man I knew might be gone forever.
D says that she'd rather not know about his new life, either, though. Although she likes the nice restaurants he takes her to. And the effect on the kids is just awful.
Edit.... was thinking about this, and realised that I could go on and on. Each thing we have to deal with seems to be the hardest part.