In my opinion, the fact that he lied to you about this is good enough as proof that he is cheating or planning to cheat. If you confront him, of course he is going to lie.

My advice: snoop. Check his phone would him knowing and look at him convos.

But if you decide to confront him about it, dont ask "do you know this girl?" or things like that. Just tell him you know that he plans to meet this girl and cheat and you're giving him a chance to be honest and tell you everything. I wouldn't expect him to be honest tbh, he will most likely lie no matter what you say.

Tbh if I were you, I wouldn't need any more evidence. I would act like normal, take my time to save money and find a new place, then move out and break up with him. I would take full advantage of him and would not let him know that I know he's cheating. It's up to you though.