“There is a qualitative difference between child support and spousal support which is reflected in the authorities, especially when dealing with retroactive support. The former is the right of the child, and unreasonable delay in enforcing that obligation is merely a factor to consider in the exercise of the court’s discretion: D.B.S. v S.R.G, 2006 SCC 37 (CanLII), at para. 104. There is no automatic entitlement to the latter. Retroactive spousal support claims require a more principled assessment of the evidence in light of the differences underpinning child and spousal support principles and objectives: Kerr v. Baranow, 2011 SCC 10 (CanLII), at para. 207.”