The document did not answer my question. My question is where is the line between cheating on my wife versus trying to get to know a second woman to potentially make her my wife.

As per Shariya rule only when a husband wants to marry with the niece of his wife he has to get permission from his wife first then can do Nikah or if his wife had set a condition that that he will not get marry to other than her and a husband has accepted this condition before doing Nikah with her.
Otherwise he is free to get marry 2nd, 3rd and 4th time but as the Quran clearly says your are allowed to do so if you can maintain “justice” amongst them. Now we should not take this task of just as an easy case. Maintaining justice means what? If anyone has failed ultimately he will cheat but it would be possible after marriage either he is maintaining justice amongst them or injustice with them. So as for as 2nd or 3rd marriage concern we can’t say itself as he is cheating with his wife if anyone wants to get marry again.
But if Islam has given this authority to men to get marry 2nd or 3rd and 4th time doesn’t mean that men have gotten this permission to flirt or having illegal relationship with other woman. This is of course haram and a kind of cheating to his wife.