I have also heard - "he makes me feel safe", and "i feel like i've known him for a much longer time than I have".

Soulmate BS. The sad/funny thing is the fact that it is an affair makes their relationship stronger. They are constantly trying to reduce their guilt by telling themselves all these 'soulmate' lies. (until they are free to invest fully in it, and realize the OP has all the same faults if not more than we do)