Relationships begin to "stabilise" once the honey moon phase is over, and there is less of a chemistry pull towards each other and you view the person in a more realistic light for who they truly are.

Anything from 6 months to a year.

When you realised the first girl wasn't the one for you it probably gave you a bit of a fright and you're replaying this scenario in your head and way over analysing it. Be aware of when you do it, but find a distraction of sorts so you're not focusing 24/7 on transposing the feelings of what happened in your first relationship to all others.

What was your relationship like with your parents/siblings growing up?