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Whitelock (28) became the latest All Black and Highlander to announce he would head offshore after the World Cup.
He has signed a three-year deal with French club Pau, the same club his Highlanders co-captain Ben Smith will head to, also after the World Cup.
The No8 said it was time to seek something new and there was plenty to weigh up before he decided to head off.
"It has been a hard decision for us and we have been going through the process for a while. This is my ninth year of Super Rugby and I'm not getting any younger," he said.
"This will take us through to when I'm 31. I know in life some things are not guaranteed and we can just control the next couple of years. Just look for a different experience, a life experience. Pau was a great fit in terms of where we could have that overseas experience."
But there were some long nights weighing up whether he should stay or go.
"It was extremely tough. Ever since coming down to the Highlanders, they have been outstanding for me. I thoroughly enjoy Dunedin people and the club. It was not something I took lightly."
Whitelock said the New Zealanders at Pau, including Colin Slade and Benson Stanley, and coach Simon Mannix, was an obvious attraction for him and he had spoken to players at the club.
He married wife Claire last year and said it was a joint decision.
"At times there is more than life than rugby. And we are looking for a bit of a life experience. If we didn't do it now ... you can get injuries. The reality is people do get injured. We just thought "take it in our own control and get away."
It took a while for it to get sorted but was now glad the decision had been made and he could get on with the rest of the Highlanders season.
As for the move overseas impacting on his chances of making the World Cup squad, Whitelock said doing the job on the paddock was what mattered.
"You could read into it one way or the other but at the end of the day if you are performing well and put your best foot forward then that is all you can do."
Kieran Read announced last week he is heading to Japan at the end of the year leaving a gap at the back of the All Black scrum.
"It came back to what my wife and I wanted to do.
`You could argue staying is a big opportunity.
`We just felt by going away was the thing to do."
Whitelock had knocked back offers previously but could not turn this one down.
His older brother Adam Whitelock played in France. He is now back in Christchurch. Older brother George played briefly in Japan but is now farming in Manawatu.
Sam Whitelock is back in the Crusaders line-up tonight but may take up an overseas contract next year.
Already departing from the Highlanders next year for overseas clubs are fellow loose forwards Liam Squire and Jackson Hemopo.