Cheaters are notorious for making up arbitrary rules that “allow” them to date even while still married.
They think if they decided (whether or not they commicated this to the faithful spouse is unimportant to them) the marriage is over then they are free to see other people.
This is not so.
If you are married, you are not single!
The promises of the marriage are still valid until a divorce is obtained. An honorable person honors such promises.
But that is the problem with cheaters.