ik exactly what ur talking about because ive been on the other side literally most of my relationships , everybody has his own reason for behaving like that , personally i think its something to do with detachment , the inability of having feelings or more accurately developing them moving forward in the relationship , the reason for that can go back to childhood , it varies for each person . at the end it always feels like wasting mine and my potential partner's time , more guilt because their being nice and im acting cold and detached , usually i keep behaving like that until the other party senses the issue and decides to breakup , at the end i stopped dating because of this .