It can be the smallest change - for instance this evening I had arranged with my partner to meet him straight after work at his mothers house. His mother lives in the same city that I work, so I was going to get the bus straight from work and meet him there, expecting him to be there - because why would he arrange to meet me there if he weren't going to be there? Anyway at 4pm I randomly text him asking him what time he would be at his mums and he said 6ish, baring in mind I finish work at 5pm and his mums house isn't too far from where I work - also when my partner says he is going to be somewhere he is usually later than the time stated. So it meant I was going to be turning up at his parents house without him, which is not what we planned - nor what I wanted. So it's sent a massive spanner into the works. I text him telling him I didn't want to be there before him and he told me to hang about in town and get a later bus. And yes I can see how this might work for 'normal' people - but for me 'hanging about' doesn't even exist in my world. I'm extremely anxious in public places and after wearing a mask all day at work I just want to hide asap. So it sent me into a funk. I ended up telling him to go to his mothers on his own.
And here I am, in such a down mood and I can't even explain why. Usually I am good with deciphering my moods, figuring out my triggers and why they might have triggered. But this one I'm clueless. I can't stop thinking about hurting myself, and was crying on the train home, I couldn't even look anyone in the eye on the train because I felt so ashamed of myself - thinking they would be too. And why? I don't know.
This happens quite a lot with changes in plans or situations. Because of this, I keep a diary so I plan things ahead in order to stop this from happening, but I can't plan everything - life is life - so it'd be better to figure out why I react this way and how to deal with these feelings rather than planning my entire life to a T.
Does anybody else experience anything like this? Does anyone have any ideas why I am like this/what could be bothering me?
I know it's a pretty silly thing to do to be asking others how/why I am feeling something, but I am really that clueless and I can't seem to help myself when I'm in this mood. It's just a downward slope.

Any input/help is greatly appreciated. Thanks for reading. xx