Should she be mad

This is regarding my mom.. and her husband. Yesterday my stepdad went to work and after work his friend and his wife invited my stepdad and mom to dinner but my stepdad was already with them.. so my mom said no.. my stepdad ended up going but his friend’s wife took a friend along. My mom was mad because it didn’t look right.. she injured her knee and can’t walk.. we’ve been tight on money and he does along buying them dinner and that other girl?? Anyways he gets home at 10:30.. and he said he didn’t do anything wrong but an hour later complains that he has no money for rent which is due tomorrow.. I try not to get in their arguments but oh hell no I wanted to rip off his face because I saw how upset my mom was.. I don’t know what to do.. i don’t know how to get my mom out of that relationship