Is OTHER wrong in the post ? POST : Theres a few parts to this so bear with me

Ok so I have pretty bad intestinal issues. At least from what I've heard. Not sure what it is or how pronounced it is because going to the doctor isn't really in the budget  but when I need to shit. I NEED to to shit. And it's not very friendly with when it wants to act up. So naturally it's pretty embarrassing and I don't really like going to other places for extended periods of time, especially sleeping over at another person's house (unless it's my parents house or I'm house sitting or something). 

Last week my fiance's grandfather died, leaving her grandmother pretty lonely. No one really comes over to stay the night anymore and she's naturally a very busy person so the loneliness is hitting her hard. 

The grandmother recently asked me and my fiance to sleep over at her house and drive her to a doctor's appointment in the morning. This is a big no from me because of the staying over part (not a big fan of the driving part but what can ya do), so I suggest my fiance does it. It should be noted here that she's pretty sneaky with what she asks and a trip to the doctor will probably turn into a trip to the doctor,the store, a restaurant, a second store can so forth. This isn't really an issue in this case, as the lady just lost her husband so it's forgivable. 

Anyways I suggest my fiance go and do it since I don't want to ruin my, and everyone else's, day with my random shitting. She doesn't want to go alone because she's not the most confident driver and the appointment is big city downtown, and also she's in a really love dovey phase since we're about to be married and besides a few things we are very much compatible, so she doesn't want to be away from me for the night.

Basically it boils down to both of us reeeaaaally wanting opposite things.

 We had a big fight and ultimately I stuck to not going and she went. I feel pretty bad about it now, but I don't think I was really that wrong in my decision. I don't regret my decision but I really regret the way it made my fiance feel. Idk man.

So am I an asshole here? And even if I'm not, am I wrong in this argument?