Any cheating Lena does at the club leads to rumors, not just Axel. Also, Lena will automatically fuck Axel at the club if you don't break his route earlier, so it's kind of unavoidable if you have her cheating.So if Lena doesn't fuck Axel at the club, cheating rumour can be avoided? I prefer cheating Lena/ Faithful Ian path but I rather Ian be oblivious to fact thn to be a cuck. It's no longer cheating if other party knows.
Note though, Ian only hears rumors from Jeremy. You can choose him not to act on them ("Ignore it" option during the confrontation with Lena) He then remains unsure and isn't technically on cuck route.