OOOOOOO luckily lol such an uncertain mind and heart arguing right now but end up I decided to keep my villagers even he wasn't my dreamie at all at first (but I guess there is feeling after such a long time together?)
If you load up the game tomorrow, talk to them and they'll bring up the topic of moving. They'll usually say "(your name) I can't believe i'm moving out in 5 days! I'm having second thoughts about it maybe I should stay?" and you get two options whether to say if they should leave or not. I don't think this dialogue comes up all the time but i'm not sure, so don't quote me on that.
Wanna something funny that can happen too?
When you WANT them to move indeed, sometimes when you choose yes they just say 'You know what, I need to made my relationship stronger with you, I'm staying.'
Talk to them a zillion times until they bring it up again, because for the next 4 days they'll still only be thinking about it. The day of you're screwed, but before then, they'll bring it up in normal conversation, giving you plenty of time to keep them- provided you play everyday.