Honestly how quickly I forget about a loss depends on how invested I was in the outcome, which is probably the case for the majority of people. There's some losses in life I'll think about every now and then in a "life would have been quite different" way but they never dominate my thoughts so I think I'm doing quite alright.
Exactly, I like your opinion, and rationally, how quickly a gambler forgets a loss depends on how much they bet and how seriously they take the outcome. Simply put, if they have high hopes of winning from the start and bet an amount they can't afford to lose, the loss will be a very painful moment and, of course, difficult to forget.
This is why we are always advised to only gamble with small amounts. The reason is clear: it makes it easier for us to forget the next loss and also prevents us from getting emotional when we lose.