Most Helpful Guy
I would say date them for a few months. It's not possible to come up with a fixed range for everybody. Different people open up differently and accept differently. However, the average stats show that dating someone for a few months 6-12 should give you an overall feel of what he's all about. But having said that, people date for years and still struggle to know enough about their partner. It all depends on the quality of the relationship. People open up quicker if they love, trust and are committed to the relationship. That's the key :)
Most Helpful Girl
It's honestly one of those things where you just know. It's different for everyone. After a couple of months of dating or something, you do begin to know them. You begin to be able to read each other's minds. But I kind of think you just know when there's a certain moment... Like if he's upset and you can just figure out the exactly problem without even asking or something.