Paul, thanks for the tip, but a bit too late since I already bought the train tickets haha. I searched for flights on kayak.com and fly.com so spanair didn't show up. But actually, I think I'm better off with the train tickets.
Spanair is charging 110 euros for 2 people, plus the cost of a hostel, it would be 160 euros total, 10 euros more than what I paid for the train.
If I took a morning flight instead of a night flight, so that I wouldn't have to pay for a night in the hostel, I wouldn't get into Seville until noon, so I lose about 4 hours compared to the train.
Gaining an extra 4 hours at the expense of 50 euros is worth it IMO because who knows how many times I will get to go to Spain again in the future.
edit: wow, vueling is only 70 euros -_-. I can't get a refund from renfe from their website and I can't call them because their lines are always busy. Oh well, they would charge at least a 50% refund anyways.