The 'All the Lovers' hitmaker – who has been dating model Andres Velencoso since October 2008 – realised her current relationship was strong because of the way the Spanish hunk was able to cope when he joined her on the road.
She explained: 'There is a big test with me and boyfriends. It's when I am on the road because that's when it's most difficult.
'Andres was around for a bunch of the North American tour dates. And I didn't have to worry about him.'
The 42-year-old star – whose previous boyfriends include actor Olivier Martinez and late singer Michael Hutchence –admitted Andres' laid-back attitude helps her to stay relaxed in their relationship.
She told Australia's Sunday Telegraph newspaper: "He took care of himself. He's very independent.
"I've had boyfriends who have stressed me out - and he doesn't. He's easy-going, funny, loving and really supportive."
The singer recently revealed her secret to relationship success is the strong friendship she has with her boyfriend.
She said: 'On top of everything else, we are really good mates. We have so many things in common, from loving to dance around the house together, to going out to fancy places to eat.
"We both love a bit of luxury, but are just as happy to mess about."