I suppose if the kind of proof you're looking for is someone standing in the bedroom and watching, MAYBE there's no proof. But here:

https://www.newsweek.com/how-many-times-trump-cheated-wives-780550

https://abcnews.go.com/Politics/list-trumps-accusers-allegations-sexual-misconduct/story?id=51956410 (These are "accusations" of "sexual misconduct" rather than longer-term consensual affairs, but I think they are credible. And sexual misconduct, which includes rape, is worse than an affair.)

Cheating on Ivana with Marla Maples has been established. Even he talked about it.

As to Stormy Daniels, it's a mess. Her lawyer, Avenatti, defrauded her (and was either fined or went to jail for that, I don't remember which), and her case against Trump was thrown out due to Avenatti not filing something legal that he was supposed to file. That's why she lost--and why she gave up.