I'm Having Massive Anxiety Over a Year Old Event, and Maybe I Need Some Advice

Quite literally.
About a year ago, I was dating my first love. (Only love?) I was mad in love with this kid. I like to think that I was able to keep most of my wits about me, but... who knows. Me and him, it was a two-and-a-half year thing.

Objectively I know, he's always been toxic for me. I know that it's good that we're over and I'm not going to go back to him, not even if he begged. He was mentally abusive and manipulative, going so far as to use one of my own fears against me.

A year ago today is when he told me that he needed 'space.' A year ago yesterday was when he got angry at me for wanting to be around him, enough to be around people I didn't particularly like. I wouldn't even remember this, if not for that stupid "On This Day" feature Facebook has, which reminded me by showing me all the posts I made about it, and reminding me how freaking anxious I was. I've been dissociating pretty hard all day. I feel removed from everyone, and everything.

I didn't want to go to work today. My MIT asked me to take over the rest of his shift because he wanted to go home for some reason or another, and I just remember thinking, this should bother me. He does it a lot. And while I do like making more money, I wasn't particularly interested in staying, because I didn't care. I didn't care at all. I ended up staying anyway.

My best friend wasn't really talking to me when all of this went down. He doesn't know about the spiral I went through when all of this happened and I'm not sure if I should tell him? I mean he's my best friend, so I should talk to him, I should be able to talk to him because he's probably the only person who could help me at this point but I just feel like I burden him all the time.

Should I tell him? I'm not likely to tell anyone else. B's usually pretty good at helping me when I'm anxious, in fact, he's the only person I talk to about being anxious and depressed and all of that. I feel guilty at the thought of not telling him, but I also feel guilty at the thought of telling him. I don't know what to do.