Is it normal to lose respect for my dad if he cheated on mom?

I agree 110% that it is normal. I would lose all respect for my father aswell. I wouldn't even be able to look at him. If he wanted to see someone else, he could have done it the proper way and get a divorce first.
...but he is a man.

Can anyone say hypocrite. How can your dad present moral authority toward you when he has his morals compromised?

It is VERY normal to lose respect for your dad. He should have never did those things. I haven't lived through this situation, though, so I can't quite give you accurate advice, but the best thing to do is to stay strong and try not to make yourself look small, you want to tell your dad that you're not small and defenseless.

So tell him! He deserves it!

Thats perfectly normal. Not only did he break her trust, but he broke yours. Theres nothing wrong with being pissed off and resentful for a while, but whats not normal is if you don't let it go. I know you probably don't wanna hear this, but eventually you're gonna have to forgive him for it. If your Mother has, then you can too, and if not eventually it'll drive you crazy and eat you up with bitterness. So who does that hurt more? The guy who cheated who doesn't have a care in the World, or you, whose holding onto it and can't move past it?

If my dad cheated on my mom or vice versa, I would turn against them.

I have a simalar issue with my dad and mom, dad meets ugly lady, thinks nice, sleeps together before devorce, its therapy to her because she's a "rape victom" my dad says, devorce, dad is controlled by lady, starts hating family, then I tune him out FOREVER for being a total dick to his only family and my mom is happy with her new boyfriend and everybodys happy btw its normal b

I don't know what, if anything you should do about your dad.

Seems you are a support & comfort to your mom. Thats good. But yes, it is normal to lose respect for you dad under the circumstances.

Do think you could talk with someone - a school or youth counsellor, pastor - about this? Your father's infidelity & parents' marital problems have been put in a very, very difficult position.