Parents fighing.... What do I do?

I've been having an issue with my parents lately. They are usually pretty good and only really fight (as in get into a yelling match) once or twice a month, but one of their fights really worried me last night. My mom was in a really bad mood and was running around the kitchen slamming stuff around while she cleaned up a bit after dinner. I went up to go help her but she said to just go downstairs and watch TV, so I listened to her because she was in no mood to argue. A little after that my dad comes into the kitchen and they start yelling at each other. I only really caught parts of the conversation but the parts I did really scared me. At first they were just fighting about respecting each other and my Mom was yelling at my dad to "not tell me to calm the f**k down". This didn't really bother me, but it was the next part I'm really worried about. She started talking about keeping secrets from her and to not bring "her" into my (my moms, this is just how she worded it) house. Then she started yelling at my dad about not making up stories and they came downstairs for a few minutes and watched the beginning of house, my mom obviously had been crying. After this, they went out for a walk and came back 20 minutes later with my mom still having tears in her eyes. We watched the rest of the show and then my dad took me to the garage where we have a weight set. He had me put 150 pounds on it and asked me to spot for him. When he struggled and tried to push up I had to help him up and I smelled the beer on his breath. After that we went inside and I went up to bed and thought a little bit about what I knew. It seems to me like my Dad is cheating on my Mom, but I don't really know, and want to hear what you guys had to say. There's one more thing I need to point out. For the last few months my dad has been getting calls (always from women, they're womens names like Katie, or Susan) and he says they're from work and always goes into the back room or sits in the car for 20 or 30 minutes. He's unusually friendly with these people from "work" and I didn't really think a lot about it until now. I understand that he needs to talk to people about work (he works as a social worker that helps schizophrenics cope with their disability) but these calls that happen once or twice a week worry me. I need advice about what I should do. I know there's not a whole lot I can do for my parents. If I try to talk to them they'll yell at me and tell me to stay out of "adult business", but I can't just sit around and watch my parents get torn apart. I need advice and hope someone can help me.