Search in CANLII for "spousal support remarriage material"
It seems that remarriage of the recipient is generally considered as grounds for reducing spousal support because it is a material change.
HOWEVER, if it was known and fairly certain that the recipient is (or would soon be) living with a (steady? employable/employed) partner at the time that spousal support was negotiated, then there is no material change, and so no reduction.
"when it is the spouse receiving support that remarries, the burden is on that party to demonstrate that, despite remarriage, there is a continuing basis for spousal support.
Ms. Kelly argues that her re-marriage is not sufficient to engage the court’s jurisdiction to vary the support order because it was foreseen at the time the initial order was made. In support of this proposition, she argues that she was “seeing” her present husband at the time of the trial. There is no suggestion that at the time of the trial, they were engaged or had even discussed marriage. The fact of their marriage was at best a possibility and an entirely uncertain one at that. Further, and more importantly, the court clearly did not take her potential remarriage into account when the initial order was made...
[The Judge is] satisfied that Mr. Kelly has established that there has been a material change in Ms. Kelly’s circumstances."
The above taken from
http://www.canlii.org/eliisa/highli...bc/bcsc/doc/2007/2007bcsc227/2007bcsc227.html
Also, if spousal support is COMPENSATORY (i.e. to compensate for lost earning power because ex stayed at home to look after kids) and not according to NEED, then remarriage is likely not relevant.