How do I work on very emotionally charged past Cs as they relate to an upcoming C?

I want to prepare myself for an upcoming raise negotiation at work but my Ts/Fs around my last negotiation are making things emotionally charged. How do I work on this? I hesitate to change my Ts around the last negotiation because I do like my reasons (I think?) but I also know I dont like my results (I havent actually done any models yet..)

In as short as I can make it, here is the situation:
I was hired to work a job in government that I LOVED and was paid the bottom dollar I could be for the position (because I was coming from an even lower paid government-job that I loved) Very soon I was promoted and promised a raise multiple times from the CEO (whose office I worked in), but each time my boss brought it up to her she shot him down. For about 18 months this situation did not change- I worked my ass off (I LOVED the job!) and they said they’d give me a raise but they didn’t. During this time my mom slowly died of cancer. I was also in grad school on nights/weekends. Then my grandmother died. I gave none of those things the attention I should have because I never wanted my CEO or my boss to question my value or dedication to the job. I don’t even think the CEO knew my mom died while I was working 60 hour weeks for her. 9 years later, that grief still haunts me (and is what is making the upcoming salary negotiation so emotionally charged!)

Finally I became eligible for a new civil service title with a higher pay range, and HR was narrowly able to get me into the bottom dollar salary one can make in that position- still $10K less than the woman who had my job previously was making (despite being told I excelled at the job far better than she or anyone else had done). I felt undervalued and unappreciated, but I still loved my job and wouldn’t ever consider leaving. My work was more important that money.

When the new CEO came in she gave me a $10K raise, saying I was underpaid. I soon left and came back into a different position, and got another $10K raise. A year later, a new job description and another $10K raise! I was finally making up for the difference between me and most of colleagues. Finally, I was at the highest dollar value one can get paid in my title. I felt valued.

But I didn’t love the new job. I had fallen in love with another field and wanted to move into that field ASAP. So I did the bare minimum in my job for like, a year or two. When it became clear the opportunities in the other field weren’t happening anytime soon, I started to reinvest in the job I had. After a few years I felt like I deserved a raise again and to see what was possible. I looked into what my colleagues are being paid to get an idea of what might be reasonable (all salary info is public) and I see them getting 15, 20, 30% raises in the period since my last raise, sometimes in one year! While the last administration had been stingy with raises, this one had been giving them out to seemingly everyone!

In Jan I asked my boss for a 28% raise. He said he doesn’t agree with that but he’ll see what he can do, though the civil service title will be a challenge. His solution to that will be to wait until Sept, when I will be eligible to change titles to one with a higher salary range. No response on the amount (which isn’t even entirely in his control). And now COVID makes the prospects of getting any raise bleak, let alone a 28% one.

So as I wait until Sept, I want to neutralize thoughts around my salary meaning anything about my value or worth at the job. I want to make the strongest case I can to my boss that I deserve 28%. I know the best way to do so is by pitching him a whole new job description, but I am not comfortable doing so because… I might get hired at the other place I’ve wanted to work for this whole time. But hiring for that job is put on hold because of COVID, with no indication of if/when it will be back on the table again. I’m torn.