Siamese Fighting Fish (aka Bettas) aren't tropical. They only require a fairly small amount of stagnant fresh water and a few weeds, like the OP had. In other news, definitely FYL, OP. My pet rat caught and ate my Betta. Don't ask me how.

Actually, bettas ARE tropical. They do best in waters around 78-82 degrees, and originate from Thailand. Also they live in rice patties that, while not very deep, are HUGE. Bettas, like all fish, do much better in large, heated, and filtered tanks. When they are given the right home, they can be much, much prettier than they are when seen in pet stores. They are, unfortunately, very misunderstood fish. I also know plenty of bettas that have lived to be over five years, only slowing down at the very end. Also, I think someone said they're only 3 bucks...? Those are veiltails, the most common of bettas. Some bettas, like Halfmoons, can be sold for 15 dollars, and are found at most petstores carrying bettas. Bettas found online, however, can run up to 100 dollars, sometimes more. Bettas should, at all times, have some type of covering over their tank, as they can learn to jump out of their tanks/bowls, for a number of different reasons. And then, with the cat...? OP, you deserved this so much I can't even understand why you thought to post this. While losing a pet that you love can be a harsh blow, from what I see, you didn't know squat about it (like many on here), and it wouldn't have lived long anyways. Do the species a favor and DON'T buy another one. Or if you do decide to get another one, do a little research. Research is a MUST for all pets bought, fish or not. Sorry, but YDI.

Damn straight #69. Would have been bad enough if it was "bought him a lovely new tank". Gonna cultivate that filter for the fish any time soon? Nope? Alright, fine, it's your fish...

"bettas normally live in a tank that is about 1L maybe less, with no filter or anything" -- normally, you mean in the wild? OP, I assume since you know nothing about bettas, you bought a cheap one for a few bucks. Buy another one with the money you saved on cat food today.