I think my mom cheated

I need help I think my mom is cheating on my dad . a few months ago I went on my moms phone and saw a un saved number and I read it and it said very bad things and then a couple of days later I decide to take screen shots of the number and I texted it asking then who are you and they never replied anyways later mom asked me who I texted one of her “friends” and I said I don’t remember and now we’re in the car and now another text from that number there where two very long texts to sum it up it said we could get married and saying we can run off and her last name can change yk. And after that I held my tears in and when I got home I just sat in that couch and now she’s asking me what’s wrong idk what to say I just said I feel bad.