I think my dad is having an affair...?

About 2 weeks ago on one day my dad started texting. Usually he is a call only kind of guy and always thought texting was a waste of time. Well I checked to see who else he texts now and it turns out i found this non-contact number that was sending him messages and calls, saying things like "I saved a bottle of wine for you", "yesterday was a great trip i had a lot of fun", and today i found one that said "today is my day off i miss you xoxo cindy". I don't know who this Cindy lady is but its super hard for me to picture my dad being this way even though I'm pretty sure hes having an affair. I'm in denial right now cause its so shocking to me, and Im curious to see what more I can learn. It's super hard to look at my dad the same good guy I always thought of him before and I've been kinda avoiding him lately. When he tries to be "funny" with me, I don't really joke back. The thing is, I don't know what to do. My mom and dad aren't really "lovers" anymore. I can tell and for a long time I have because my mom and dad are really unlike each other and their attraction has worn off even though they are still married. I dont want to see my mom get hurt and likely force a divorce cause she'd have nowhere to go really but at the same time if I keep my mouth shut I always think about it in my mind just how bad this is while its going on and doing nothing about it when I could be doing something...you know? The thing is, if I confront my dad, i have no idea what will happen. He's unpredictable. He may just admit it in cold blood or decide to deny it completely like a fool. The thing is, I don't want to see a splitting of my parents just like any other 17 year old, because I'm afraid my life will change so much and my mom will be hurt the most. On a serious note, what should I do? Confront my dad? Wait longer and see where this goes? Keep my mouth shut?