In the recent Bishop v. McKinney case (2015 ONSC 5565), the Honourable Mr. Justice Price made a very well-written, thoroughly analyzed and fair order dealing with variation of an order of spousal support.
The Honourable Mr. Justice Price noted that an order for variation will be instituted only if there is a material change in the circumstances which if known at the time of the previous order would have resulted in a different outcome.
Further, he noted that remarriage is not a bar to the continuance of spousal support. However, he pointed that remarriage or three years’ cohabitation could constitute a material change in circumstances warranting a variation or termination of spousal support. As such, remarriage or cohabitation of a former spouse may constitute to be a material change in the circumstances validating a variation of a previous order.
http://www.canlii.org/en/on/onsc/doc/2015/2015onsc5565/2015onsc5565.html#_ftnref26