So the other wallet has also been yours I guess?
Well that really sucks.
This is the reason why I always check 3-4 times if the address is correct before I hit the send button.
Humans make mistake.
And how much is a "decent amount" in your case?
I think majority of us have done this mistake, this are the basic things we need to learn and we need to learn from our mistakes, if the amount is small won't make any difference but if the amount is big then you would regret on your mistake for entire life so its better to recheck the BTC address before sending or receiving.