I am POA for my live-in friend of 20 years who has ALS. I can't take the verbal abusive words anymore. Can I just up and leave?

Join the patient at the next doctor's appointment. S/he is likely suffering from depression, which can and should be treated. If the abuse is new in your relationship, it may be a symptom of the ALS. Bring this up to the practioner to get help from your friend. Also, there are ALS support groups that you might participate in together. Up and leave, should be the last step. I helped my friend through a 7 year bout of a slow version of ALS. Most times, the patient has passed much more quickly than that. And yes, she was on anti depressants for a good part of that time. It helped her and as a result, us .

Up and leave? Not sure what you mean by that....also, it depends on your relationship and what you agreed to do to assist your friend.
If you are suffering from verbal abuse, then you need to protect yourself. However, please transfer the PoA to someone else and see that your friend has help in place before you leave.