The following advice is aimed at adults who have been dating for a good decade already. In my opinion, you should do whatever you want with dating in your twenties, within the bounds of treating people with feelings like you would want yourself to be treated, of course.
The proverb ‘All’s fair in love and war’ is never literally true, but is whimsically true when you’re dating in high school and becomes less true the older you get and the more you should expect of yourself and others. When you are young, too much about your core self is malleable, and that’s how it should be. Other than those occasional high school sweethearts who got lucky and have been together ever since, dating in your twenties should be viewed as an experiment to find out what you want out of a partner, and what you are prepared to offer yourself.
However, at a certain point you need to get your romantic shit together. In a sense, every romantic relationship you will ever have goes through a “high school” stage in the beginning, during which you’re just getting to know each other and it’s OK to find some unforgivable deal-breaker, and break up with caring, but without much else owed to the other person.
This ends after a couple of months. The longer things go on, the more you will “owe” the other person. If you’ve just ghosted someone you’ve been seeing regularly for six months, unless you did it because you fear for your personal safety or something, you’re not a kind person.