In short : It’s good not to forget, but if i never forgive then i’ll always find a reason to hold a grudge against someone. I prefer to have Saudi Arabia with us than against us(, the same could be said of any country), not you ? It’s up to north yemenis to hold a grudge against their support for south Yemen, but your criticism should be primarily directed at the south, and understand why the north acted like they did as well.

As a prelude for the longer answer below, i “know” just enough to understand that it’s complicated, because they have a long history which needs to be understood in order to grasp the causes, i’ll stop hereafter at their revolution of 2011 but i’ve absolutely no doubt that we would need to go further in time.
It’s interesting to note that we(sterners) were supporting the royalists against the republicans in the long civil war that started in 1962 b.t.w. I have suspicions that, back then, Saudi Arabia acted in order to avoid being “contaminated” by republicanism(, like european countries after the french revolution, the west with socialism, or, supposedly, current oligarchic governments with an hypothetic direct democracy, as well as some states/civilizations towards other religions such as the anti-islamic propaganda during the middle-ages(, or internal schisms like protestantism//catholicism), etc.)

The Houthis are against Saudi Arabia, it’s in the interest of the latter not to let open enemies proliferate at your borders. On the other side the Houthis(‘Ansar Allah’/“God’s auxiliary/supporters”) have a vision for a Middle-East independant from the west and were actively against the invasion of Iraq, if i understood correctly.
I won’t continue this post, just end it with saying that if Saudi Arabia is united with Iran, if the North&South are allied with them and each other, and other countries as well, in a diversity which accepts the republicanism of some countries and the royalism of others, who even celebrate it, then these causes would cease to exist and these wars could end, everyone would gain as much power as if they militarily invaded every other country in the alliance, the only difference would be that these countries wouldn’t end up as uniform/homogeneous ^(, at least not immediately, some contamination and progressive uniformisation may appear if effective counter-measures aren’t taken). We’re not uniting for reasons that i’m still searching for, and there’s certainly solutions for them, i can’t believe that conflicts&wars can only be solved through a homogeneity afraid of any possible internal schism, and progress.