Yeah, it sure sounds like your moisture-protein balance is way off if your hair is breaking off like that. How does your hair feel when it's wet? Is it "mushy"? I've never actually had mushy hair, but I read up a little about it when I wanted to understand what the heck the term referred to. Mushy hair indicates over-moisturizing and you then need to have protein treatments to counteract that. Does your hair feel really "hard"? Protein treatments in that case would only make it harder and break off more. Getting that balance back would hopefully help a lot with what you're experiencing.

I agree with the suggestion about using a heat protectant if you're going to straighten your hair with a flatiron. I used to flatiron my hair and never even thought about using a heat protectant. No idea what I was thinking.
3b / Fine / Low (to Med) Density / Normal Porosity & Elasticity

Currently Using [*Holy Grails*]
Cleansers: DC No-Poo / DC Low-Poo / *BaSo & ACV*
Co-Washes/ROs: CJ Beauticurls Argan & OO / DC OneC / Organicals DC Creme
Additives: *Silk Amino Acids* / Honeyquat / Fragrance Oils
LIs (found some!): KCKT / CJ Beauticurls LI / CJ Curl Assurance Smoothing Daily Condish
DTs: *Coconut Oil* rinses / *Honey*, EVOO, & DC OneC / CJ Curl Rehab
Sealer: *DM Super Buttercreme*

Goal: APL Hair