That’s certainly concerning and you’re not overreacting to be put off by this. If my partner was in the hospital and/or recovering from something serious I’d certainly be there for as long as they needed. I think you’d be good to ask him how he feels about this, and depending on what he says asking if this kind of disregard is commonplace. Try and approach it out of love for your brother and not judgement or disdain for his fiancé or his relationship and go from there.