Ugh why am I like this

So for some reason I fixate on things, and when I say things I mean like physical items. For example there’s this consignment store I shop at for my kids, since covid happened they’ve made it so that you can order things from them online. Well a couple of weeks ago they posted this shirt, it was a Nike Kobe Bryant retirement shirt, I had put it in my cart to buy for my son but completely got side tracked and forgot to purchase it, then I decided to hold off until next payday, I mean it was only $5 so I’m not sure why I decided to wait, and because I decided to wait one extra day the shirt sold, someone else bought it and it’s literally ruined my entire day, I feel crappy, I feel sad, I feel angry with myself, I’m all of a sudden in an incredibly horrible mood. I looked the shirt up online to see if I could buy it elsewhere and sure enough this thing is discontinued and is selling for over $200 which makes me feel like even more of an idiot for not buying it when I had the chance. My question is why am I letting things ruin my day, it’s a damn shirt for crying out loud, I have no idea why this kid of stuff gets to me so much. I really wish it didn’t, I wish I could just say oh darn we missed it, too bad, and go on with my day. But I can’t, I can’t stop thinking about it and beating myself up for it. And this isn’t the only time this has happened, it happens quite often when I miss out on something because I took too long to make my mind up.

Does anyone else go through something similar? How do you cope? I need to change my mindset but I just can’t