I don't know if I got cheated on or not
What aren't you sure about?
I found sexting texts on his phone that I don't remember sending him any.
Well, you should confront him about those texts. Trust and loyalty in a relationship is crucial for it to last.
No, he's a liar and he is cheating on me. I'm going to get revenge on him.
I understand why you would be angry but getting revenge is petty and a waste of time. A cheater is never worth it. The best revenge is moving on and having a happier life without them.