Just for context, I was a math major in university and have used math in my job on multiple occasions.
To me reading math yourself is something that you do for fun, if you find it to be fun. Whether I personally find it to be fun might depend upon which day you talk to me and what sort of advanced math is involved.
Math is a subject where what you are learning now depends a great deal on what you were learning last year, and what you are going to be learning next year will depend a great deal on what you are learning now and what you learned last year. This means that it is very important to have a solid foundation. You want to learn every step very well.
Just to give you one example, I recall a couple of very difficult math problems that I needed to solve on the job. One required quite a bit of multi-variate calculus and stochastic processes (the latter is something that you take after first studying probability and statistics). However solving this tough math problem also required a lot of high school algebra and in one case trigonometry. I needed to be very solid in high school algebra in order to be able to solve any of the toughest math problems that I have ever needed to deal with. What this means is that when you are studying high school algebra you are learning things and developing skills that anyone who is good in math is likely to need to use a lot for many classes in the future and potentially on the job in the future.
And I think that you will learn math much more thoroughly in a class, with a teacher, and with exams that you can use to judge how well you really understand something.