Mom cheating?? What would you do?

My parents have been married for 39 years on September 19th. They have 8 kids and my mom works full time plus has her own business and my dad has his own business so they tend to argue and fight alot cause my dad is horrible with communicating. Anyways the other day I was trying to fix my mom's phone and her text messages popped up and someone texted her saying "do i get a dressing room pic;)" I don't know if it's from a girl or guy. I know she's been talking to this person for years and they text her saying "i miss you" and they will text her multiple times if she doesn't answer..so I want to know does it sound like she is cheating on my dad? And if so should i say something to my dad or just leave it alone?.

Update: So some people say I don't know the kind of relationship my parents have but I do. I live with them. My mom says it's ridiculous how my dad flirts with the women at the bank. It's gonna be Tmi but I also know they haven't had sex for almost 16 years. The person she is texting is a guy. I found out that his wife died 2 years ago. My mom met him and his wife on an online music group for a band they liked over 10 years ago. And he does know she's married and has kids. And he flirts with her alot it's not the whole "I miss you text" that bothers me it's the whole situation. Like who asks a married lady for pictures of her in the dressing room. And my dad has no idea she talks to this guy. And he calls her only when he knows she's going to be going to work. I just don't want to hurt my dad. And my mom has said she doesn't want to divorce m dad but they have a very strained relationship.