How do you disconnect from the past if things weren’t meant for you?

I don’t know really any solutions to heart break, but well over the time for me to move on. I was broken up with 7 months ago, and it took lots of time to heal (year long relationship). He immediately went to other women, and you can imagine the whiplash of someone you loved deeply turning into someone completely different. Today, I saw my ex’s Youtube video of a game posted. I guess I forgot to unsubscribe, since he hasn’t posted since we broke up. Anyhow, even seeing the name triggered me and made me pretty upset (I proceeded to unsubscribe and not even watch the video thankfully). A mix of loss, and nostalgia. I haven’t been able to process or grieve things like I want to because of high school. Now that I am a senior and out, it’s starting to come back in waves. I guess I miss the connection, or something. I’m pretty alone now, and it hasn’t really hit me until this moment how alone I am. It feels like there is really nobody who shares my interests.