Oily, frizzy, over processed hair... what do? Please help!!!

WARNING! WALL OF TEXT! sorry :(

Idk where to start so I'll just go from the beginning. My natural hair is super boring dark frizzy/wavy brown with thick strands but sparse growth... I've always hated it. That being said, I've manipulated it a lot and for the second time in 5 yrs it's so damaged I don't know what to do. A little back story, I had it platinum before and the girl didn't wanna damage it too much and so we just developed and toned it light for 3 hours at a time... I know now from experience it was a bad idea it was to do that. Eventually it was just so fried I chopped all my hair off into a pixie. I kept that for about a year until I really started to yearn for a ponytail... also it was kind of a pain because my hair is so unruly I HAD to style it daily and I thought it made me look boyish so I felt obligated to wear makeup all the time. It got tiring, so I began to grow it out again. Inevitably, I got bored with my ugly mundane brown mane so I dyed it a rusty red. Then I really wanted to do something fun for my 25th birthday so I decided to have it done blue and green, but the red was a bitch to get out so we had to bleach twice then color it in a third session over the course of 6 weeks. When I got tired of the blue and green I wanted to go back to ashy blonde/taupey grey but the blue and green were even more of a bitch to get out. Over the course of several sessions with my hairdresser and a lot of tlc we got my desired color and decided to blend my dark roots in for an ombre kind of effect. I'm pretty happy with the color and feel that it really suits me but despite my best efforts, my hair is rekt. By day three of not washing my hair it looks and smells disgusting from all the oil. Even though I let my hair mostly air dry, blow drying still takes like 40 min. But if I don't blow dry it it, it dries super scraggly and the ends break off like crazy. I try not to wash it often, I condition regularly, for a while I was using an at home olaplex treatment, I've tried dry shampoo, dish soap, sulfate free products and natural oils (avocado, coconut, jojoba, and argan), I try my best to avoid using irons, I've tried different materials to wrap my wet hair as well as different brushes to prevent breakage, I get regular trims..... ugh I am at my wit's end. My current hairdresser is a great gal who really knows her stuff has suggested I do a keratin treatment. She said it lasts 6 months but it costs $300. My best friend insists that it's a bad idea and that I should keep trimming the damaged hair out and then start over again but I DON'T WANNA 😢😢😢 It's taken sooo long to get to the length and color I have... constantly trimming it would eat away at my soul to never gain length and working in slow sessions to get back to this color would eat away at my wallet.

What is your opinion? How do you feel about keratin treatments? Do you have any suggestions for how to fix my hair? I am so so so so sad over this!!