How to balance emotions and self-regulate better?

If I could add two tags this would be a vent as well. Apologies in advance.

I (20F) have been noticing that I've been becoming a worse person by prioritizing my emotions and my own experiences and mental health. It's affecting how I talk to my partner when I'm upset, my study life (in University), and just my daily energy.

Due to trauma in my past, when I was a teen I bottled up emotions to an unhealthy degree. I went to therapy to unlearn that and to learn how to safely let my body process my emotions so that they wouldn't explode over time. However, I graduated high school and felt like I didn't need therapy any more since I was feeling great. Only problem: I never learned to self-regulate, only how to feel. Plus, I was a loner and none of my emotional outbursts really affected anyone else to a high enough degree that I felt was necessary to change.

Now I have a wonderful partner. He is incredibly emotionally mature and self-regulates better than anyone else I've met our age. I feel like I don't treat him right due to my inability to self-regulate. It ruins everything: when we get into small arguments I get overly butthurt and shut down. If something bad happens, no matter how small, I blow it out of proportion and spend the rest of the day tired and upset. This is even more relevant now that one of my family members got diagnosed with cancer and everything seems much more catastrophic when something small goes wrong. I take it out on him by picking petty fights, and only then realize that I've been very unfair to him and apologize.

I struggle to find a balance between "it's okay to feel your feelings and it's understandable that little things feel worse cause of stress and grief" and "how could you be such an asshole and let your feelings dictate everything." I only know how to let my body feel my emotions at 1000% strength, or not feel them at all. Both ways are unhealthy and take over my life.

I wish I could go to therapy for this, but right now that's kind of difficult as I'm constantly moving around and don't have a job to pay for it. Maybe someday soon.

tl;dr: My emotional regulation skills are ass and I keep flip-flopping between blowing up and emotionally shutting down. I want to change this since it's affecting the people I love. Can't get therapy rn. Tips? Anything helps.