How do I do This?

It's been 2 years since I've been with my SO and i'm seeing more and how his ADHD is affecting us and my son ( different dad) .
 Most recently it's been financials and i get that we haven't had much coming in and have had to move funds around to manage/budget the household. 
So I had put paying my phone bill off a few times, so we had money for groceries. Every time we talked about payday i had it in there to pay and then a week later i would still have the funds in my account and tell him, "i'm not paying my phone again, don't worry. " Now he's coming at me like" why did you never tell me this, you have to tell me this, we need to have a working budget that includes ALL of our bills." Which yes I get, but he had agreed full well, if it comes to phones or food, the latter will be chosen. I can't stress to you how frustrating it is that he doesn't remember those conversations. I feel like i need to write everything down that i say so he can refer back to it when he gets likes this, we are very slowly getting ahead but when he gets so upset, I barely have the energy to argue with him about it. these instances happen all the time and i will admit fully that i have a bit of mom brain, but I know when i tell him. 
I feel like i'm getting gaslighted constantly when it comes to communicating with my guy. 
I Love him so much, but i'm beginning to feel alot of resentment.

Feeling helpless.