I'm always amazed when people who make music by ear think music theory and harmony, and music sight reading and ear training is a great mystery and must be really hard.
GEEZE! It's not like you have to INVENT music theory someone who it was taught to has to show it to you.
That's it!
If you are really serious about studying music theory online I'll give you your first lesson free to show you it's not that hard
When I taught kindergarten through 12th grade I had my 3rd graders doing music theory