I am currently playing a family and my man Tristen is having a midlife crisis and has had a couple affairs that resulted in some new branches on the family tree. In my mind this is because his wife Ellianna is going through menopause and has little to no sex drive. I have searched custom traits and there are Nympho ones and all sorts for those SIMS that just cannot get enough woowhooing in their lives, but I cannot find one for those SIMS that really just don't like to woowhoo. I mean they do it because it is a healthy part of any marriage, but they don't really like it. I have downloaded the SIMS Buff and Trait factory, but have been unable to figure out how to do anything other than create the words. Does anyone know if there is a custom trait out there like this already? or a really good in depth tutorial to creating a trait with buffs and such?

If you got around to downloading the factory, there should be a tutorial with it as well, so you should read that too.

Theres the Unflirty trait from the City Living expansion. Never used it myself, but I imagine that sims with it will reject romantic interactions like woohoo.
If you want them to accept and like...get a negative buff or something after woohoo...I think you'll have to put together your own trait for that.