Hello, today I am about to tell you guys something I feel horrible about it...
So, I looked at my betta's 1/2 gallon tank, and it was dirty so I knew I had to clean it, at 10:00PM or so, I brought him in the kitchen I let him look at the glass cup, at first he was REALLY scared of it until he went on top of it, then I was able to scoop him up. I rinsed out his tank and then his gravel 3 times, hit gravel would make the water horrible so I decided to change it with new gravel, I rinsed it out in in hot water. A few weeks ago I broke a plastic cup, so I went to my couch and grabbed the broken plastic cup, I rinsed it out in hot water... And then I added Aqua-Plus the conditioner was watery? And I only had it for a month or week. I put him in and he was fine, then I put the plastic it cup in then he started trying to swim as fast as he could, so then I put him back in the cup and then he was okay in the cup then I took out the gravel rinsed out and the cup for a few more seconds I put the cup in and put the gravel over it, the gravel held it down, I put the water in then I poured him in then he was going crazy, swimming and hitting things then he started going upside down I grabbed the cup threw it out, scooped him up. But it was too late, he was facing up, not 100% upside down, he moved a bit, then stopped. I tried to see if he was still alive, but he didn't I netted him and put him in the toilet and you know the rest...
I was wondering what could of effected him? Was it the cup, the conditioner, or just stress?
I am so upset, he was my second ever betta and I only had him for a few months, I loved him, he would watch me when I was on my computer and he just started to trust me, I remember when I got him from the pet store he was so small. Now I only have Moon my HM, I just lost my CT

Do you guys know what could of effected him?
Losing him was horrible, I loved him so much but I could tell he was getting fin rot, a bit, I was getting him a 5 - 10 gallon tomorrow... I shouldn't of touched the water i'm so stupid....
I believe he may of been 3 - 8 months old... Don't believe I lost him...I'm such an idiot, why did I change the water argh...