Well, here's something to avoid in a happy relationship. And I believe it happens more often for individuals who are truly in love, which is a heartbreaking paradox.

It's a line from William Shakespeare's Hamlet. "Where love is great, the littlest doubts are fear; Where little fears grow great, great love grows there," he says.

And what he means is that when you're in a happy relationship and actually realise that the other person truly loves you, your instinct is to be worried because if it's true love, they could break you unbelievably. You almost feel it's too good to be true. How could somebody love me that much?

You start becoming suspicious and  superstitious, as if you're looking for hints that something is amiss. It's as if you want to prove to yourself that you are unworthy of so much love.

Therefore, paradoxically, a hallmark of deep, profound love is precisely this feeling that it is too good to be true.