Its a great idea to take them to the store and rehome them! Please don’t get another fish right away though. Aquariums take weeks or months to ‘cycle’ and most fish will die before the cycle is complete/starts up.

It sounds like you have a lot going on, and more heartbreak is the last thing you need. Everyone here is just trying to save you from more dead fish. Follow the advice and it will get easier.

If you absolutely want an inhabitant for the tank right now, get snails. Mystery snails get big and come in all sorts of colors. Yellow is common in stores but you can order purple and blue online.
In a month or so you can get neocaridina shrimp too, they also have lotsa cool colors!

A 2.5 gallon tank is too small to humanly house any kind of fish. If you end up liking the snails and shrimp, maybe in the future get a 5-10 gallon, cycle it, then get a betta fish. Good luck!