No I don't believe in 'the one', I also believe in degrees of compatibility, and that can sometimes change throughout a relationship as people change and grow from experiences. So a couple who were initially very well suited may be less well so 10/20/30 years down the line.

If you look around you can see people who either grew apart over a period of time or lost their partner through death - they can then go on to have another equally happy long lasting relationship with another person.