Should I tell my mom?

I noticed my dad has an online dating page. He only seems to use it when my mom is away for a few days. I saw him using it when I walked in and he immediatly closed the page. he left home to go to home depot about 45 minutes ago so I took this oppurtunity to go through the computer. I found his dating page, evrry bit of information on there fits him perfectly. I think it's sad because the about me says how he is looking for a mate to spend the wonderful moments of life with. I also feel like I wanna cry because it says how he has no kids, and is single. Well I know he has 4 kids and has a loving wife of 23 years. I don't know how my dad could do this, I printed out a little bit of evidence that I can show my mom when I see her in two days. Im so upset. I know that it's the right thing to do. And I'm positive she should know. Am I making the right choice?