You're right, there's clearly something wrong with David Harbour and he's not the "nice guy" he makes out to be.
I got shady vibes from him back in 2017/18 with how fast he latched on to Alison Sudol. He found her music on Spotify mid December, then followed her on IG and literally overnight he was in London spending New Year with her. Following her on that arctic expedition she went on, they got a dog, and were popping up everywhere together, then poof - they were done.
Don't think it's ever come out why they split but she moved on really quickly to Tom Cullen, and was pregnant by him quite fast, so I got the impression she was ready for a family and he wasn't, which is why I was a bit shocked to see he'd shacked up with Lily.
I dunno, but he clearly goes in hard and fast and then loses interest or can't maintain his interest. I heard he got pretty fucked up over Julia Stiles but that was over a decade ago now. I found out recently that his mum died in late 2019, so you never know what that does to someone with regards to relationships but I think it happened after he met Lily. But there's certainly something that doesn't sit right with me about this pairing.
He gives me vibes I don't like and I agree that I don't think anyone who's legitimately happy and content in their relationship/life ends up losing so much weight and just looking terrible in general. She's either trying too hard to be someone/something she isn't for him, or the stress of maintaining the relationship is literally eating away at her.
She's clearly invested a lot into it, in terms of money with that house but also with her kids. Dividing them between London/NYC because of him, if/when it goes to shit it'll fuck them up all the more to have their lives up ended again. That could be what's stressing her, the old "sunk cost fallacy" keeping them together.