Watching my ex adjust to the single life, I was actually thinking of posting something similar. I don't think my ex regrets leaving, but I do think he was shocked to find the grass isn't nearly as green as he thought it would be. Even though he's the one that left, I feel like I'm embracing my post-divorce life with more enthusiasm than he is. I'm back in school working towards a career I'm very passionate about, and the kids are thriving in their new schools. I definitely feel the load of single parenting and managing the house on my own, but at the end of the day I think my life has improved immeasurably since he left. Once the initial shock wore off, I feel like I dropped a dead weight.
I don't think he, on the other hand, thought through the divorce beyond "I get to fuck other people and go to Hawaii whenever I want!" Just months after he left, he drunkenly confessed he was just then realizing that divorcing me didn't solve everything: he still hated his job, he still can't move to Hawaii if he wants to have a relationship with the kids, and now that he gave my half and has to pay support, he's no longer able to retire at 54 like he'd planned.
Just the other day I had to bring up to him that the kids are being hurt because all he talks about is his girlfriend, and that he constantly texts her even though he only sees them 3-5 hrs per week. It's been an issue for months, but I finally felt like I had to say something when the kids came home from dinner on Wednesday complaining, "Dad only looks forward to seeing us so he can tell us about his new family." I was fully expecting to be told to mind my own business, but instead I received a hearftfelt reply that admitted he does talk about her a lot, but only because he doesn't have any thing else to talk about. I felt sorry for him . . . until I remembered that he's the one that asked for this.
So I wouldn't say he regrets leaving - it was obvious he felt trapped in this suburban life - but I'm not entirely sure he found what he was looking for either.
If I had to speculate, I'd say him diving head first into a relationship right out of the gates has been an obstacle for him. He met her on vacation, which means she's a good 10hr flight away. I know he cares for her and she seemed nice enough seemed when I met her, but I think he'd be in a different place mentally if he'd gotten involved with someone locally - or, heck, even waited until he filed ;)