Please tell me I didn't just discover that my dad is having an affair or something

He was showing me a video, and some messages on messenger from a younger looking girl appeared that said : '' Thank you for your kindness my ❤ ''.
'' I.....My tender love ''.
He quickly pulled the little circle away, but he didn't look ashamed or something ?

Does this need an investigation on my part, or should I just ignore it to not discover something I don't want to know about ?

My father is my best friend and my role model, if I ever learn he's cheating on my mother, after 30 years of marriage, I will be so disappointed.