Waiting until marriage before living together

How did it go for you and your spouse? My cousin has a very religious family (nothing wrong with that) but it’s been heavily influenced she waits for marriage. For sex & living together. She has had sex (parents obviously don’t know) so that’s what she’s done.. she still lives with her parents but is getting married late August. They’ve been together on & off for a few years. They recently bought a house together and he is currently living there while she stays with her parents until the wedding... fine, whatever. There’s already SO much they haven’t discussed or even thought about... like MAJOR things. I love my cousin she’s like my best friend. Obviously I’m not going to be like “hey have you REALLY thought this through?” I’m just worried because she has even said before she has a hard time being attracted to her soon to be husband. And when they argue it gets HEATED fast (not violent) but she gets close to breaking up with him. She’s with him willingly, parents didn’t encourage her to get married right now. That’s just where they’re at in their relationship I guess. This is not at all coming from a place of judgement. I’m just genuinely worried because I don’t think she’ll be able to go through with a divorce if she’s unhappy.. her family will probably disown her if they split up after marriage. I don’t think they’ll DEFINITELY split up. I think they could probably work through whatever’s going on but moving in with someone you’ve never lived with and it being automatically “permanent” sounds so scary to me. So many little weird habits and routines you never even consider until you’re living with that person. But I also know so many people do this & it’s perfectly fine!