With good reason it seems – according to the singer, the couple's blissful relationship is in part down to the fact they have never even had a row.
"We don't fall out, we have nothing to fall out about," the 35-year-old has told a British magazine.
"We don't have arguments, we just get on and we make each other laugh – we're a good team."
And, Robbie adds, the success of their romance is also down to the fact that the 30-year-old American "digs me and I dig her."
"I trust her 100 per cent, and there isn’t even a glimmer of worry of her only liking me for this singing malarkey," he added.
"I'm a pretty cool guy, you know, without all of that anyway!"
Robbie made headlines last month when he proposed to Ayda live on Australian radio, but later revealed it was just a joke.
He has confirmed he is not quite ready to settle down and get hitched because he wants the pair to "have more fun and not be grown-ups quite yet", but that having children is "definitely on the agenda."