Help! I feel so guilty for quitting my job?

okay so I work in a restaurant as a waitress, recently the only manager left, and as a result the restaurant is being run completely by the owner. Now, I won't say he is a bad man. But he has a tendency to yell, and can get very abusive. If you stuff up an order, he will send someone to tell you to meet him out the back of the restaurant where he will cuss and insult you. The chefs get the grunt of it but the waitresses are always being watched and yelled at also. As well as that, we have to tell customers that want to pay in cash to pay at the register not through the waitress. This is so any spare change is put into a tip box, not given to the waitress. the box gets a lot on money put into it. in 12 months working there I have not seen a cent. So last week I realised the pressure of this job was affecting my school work. I am finishing school and I really need to do the best I can. So I gave my two weeks. I didn't realise it, but that day another waitress and a bartender quit. This seems to have spurred a mass exodus, and a further two waitresses and a chef have quit. he was clearly stressed about it, little does he know that two more waitresses are quitting, without notice! I feel bad because I know I can get another job, but this is this man's livelihood, and I don't want to be part of the reason things go wrong for him. what is the right thing to do? He now has a total of 4 wait staff and a bartender... And we are a busy place. Should I offer to work every day till my notice is up? Should I stay on? Or does he not deserve it? Also do you think he will give me a bad reference for leaving the same time as everyone else and leaving him kind of screwed?