It's not the cheating, as shitty as that is. It's the denial and outright lying about it. Which was also the real issue with Clinton and ultimately why he was impeached.
People should expect more transparency and at the very least to not be lied to by elected officials. Even if they tend to be scummy. Accountability is vital.
what does it matter if a politican lies about their personal life? as long as it's legal idc what they do in their personal time, unless it affects their job
Lying about personal life while being in office, even if the event took place prior to election, is a shitty precedent. The paying off was only done during the campaign to prevent news stories and interviews from coming out, so it has relevance and potential influence to him even being elected at all.
Are you genuinely asking why people may care that the leader of their country is ok with lying on the record?
No, his personal life before he was a president isn't your business. He doesn't have to confirm or deny anything unless he wants to.
Besides, this again is a drop in the bucket of scumdom. Why are we acting like this is some breakthrough?
Low-hanging fruit. The serious charges will still take time to finish being investigated and prosecuted. In the mean time, this one's pretty much already been confirmed. It's just easy, and the public loves hearing about politician's sex scandals and infidelities. The media always swarms over this stuff, regardless of which party the guy belongs to.