Here is the reason why complements make black. Black is not the absence of all colors, that's white. The presence of all colors makes black. There are only three colors, red, yellow and blue. If we put two of these together, say, red and yellow, we make orange, a secondary. That secondary, orange is the complement of blue. Blue is the third primary and we didn't use it in our mixtures so far.
We have added red to yellow plus that third primary, blue.
If we mix blue and orange (red and yellow) we have mixed all three primaries. When you mix all three primaries you get black.
This works with yellow and purple, green and red etc.
I want to give a quick shout-out to Inez Sainz, I have no reason to believe you read my blog, but you never know. If you do, I'm proud of you, and I'm on YOUR side, I think you've got a lot of talent. I would also like to add that I'm cooler than your boyfriend.