True happiness is something that should make you happy in the moment and in the long run.

I’m not sure I agree - why is a long term aspect necessarily for something to constitute true happiness?

If I can’t remember something, does that mean it didn’t make me “truly happy”?

If so, that would mean that a child given a toy they play with for years but eventually lose interest in and forget as they grow older, didn’t experience “true happiness” from that toy, which doesn’t seem right to me.

I don’t think permanence or longevity are factors in whether ones happiness is true or not.