I'm an old so this game is decades behind me, but....
in a long term relationship, women want to be #1 in a man's attentions. They want him to be completely carried away by her in all things.
They certainly don't want to be #2 to a job.
If they sense the guy cares more about his career than her, she will be out of there...unless she is out golddigging. But that is a different issue.
So maybe what you are missing here is that yeah, they get bored of you after a few months not because you aren't 'fun' enough...but because you clearly aren't putting them #1 in your life.
This is a much better way to describe "the game" I posted earlier.