Need help with emotional regulation

So recently my long distance partner visited me for just one day and then had to leave. Immediately after, he had to attend a close friend’s wedding so he wasn’t available to talk. After that, he'll be moving to another city for work. (Earlier the distance between us was around 400km but once he relocates it'll be fucking 2500kms).

When he left I initially didn’t feel much. But shortly afterward, I began crying uncontrollably and continued until I fell asleep. I woke up with swollen eyes and felt emotionally low the entire next day as well. I am also about to get my period so my emotions may be heightened because of that.

We have been dating for only six months so I don’t think I am in LOVE love yet, but I don’t fully understand why this situation is affecting me so strongly. Since he was unavailable due to the wedding, I began spiraling mentally.

It’s not as if I lack responsibilities. I have classes from 9 am to 6 pm that usually keep me occupied. However, yesterday I felt completely overwhelmed. I didn’t cook for myself and starved to sleep. That worries me. I don’t think this level of emotional reaction is healthy.

I happen to be someone who's extremely impulsive, reactive. I rarely feel emotionally stable or balanced. My emotional state is almost always at an extreme, either very high or very low. There is hardly ever a middle ground.

The same pattern applies to my work life. I work intensely until I reach complete exhaustion. My mind does not allow me to rest until a task is fully completed, even if I am physically or mentally drained. In friendships as well, I tend to function in extremes. Either I do not care much at all, or if something affects me, it affects me so deeply that I feel like cutting the person off entirely. Overall, I seem to operate in all or nothing modes - emotionally, professionally, and socially.

I want to understand how to regulate my emotions better. This gets so exhausting I really do not know what peace feels like.