Why are females so freaking difficult to be friends with

Not all females are difficult to be friends with. Don’t look at it from that viewpoint.
Im sorry you and your friend are growing apart. But it’s not that uncommon. Especially as you were hs buds and essentially children when you met. People change over the years and grow apart. It’s life. Growing pains and what not.
It may be time to distance yourself and down grade the friendship. Give your time and effort to others.