Sometimes I multi-class... but only occassionaly as I prefer single class characters.

 

Sometimes on level up I get two points instead of just one, but I can't use them both on the same class. Is there any way to change this? I really only want one class to progress the second one I only occasionaly want to get an ability for.

When reaching new power level you gain one point in each class you picked. Points inbetween power levels can be spend wherever you like.

In a word... balance. You get an extra point when you go up a power level/ability tier. Single-class characters gain power levels faster and get to put both points in the same class. Multiclass characters have to split them up. It's the price you pay for versatility.

 

If you're looking for a way to change it, I'm sure there's a mod for that.