Hey sorry for Max
I am just wondering if you need any help? I have very good link from this forum about disinfection in case you want to put another betta in the tank. Or i can try to figure out what happened to Max. Sorry not sure how long you have bettas and how much you know about them. A lot of time betta can be just sick from the store. Any time when you buy new betta ALWAYS QUARANTINE it from OTHER FISH if you have one, or even if you don't have any other fish you can just quarantine fish in the tank with out gravel, decorations etc...just so you don't need to disinfect it later. Please let me know if you need any help. I can give a few tips on betta care, how to pick healthy betta, emergency kit in case you buy sick betta.
And do not get discourage if your first betta died, believe me it happened to all of us. To every one. So i hope you will rescue another one