Aly,
Just call him up and tell him you've decided to move forward elsewhere. I don't know if I'd mention anything about mistakes or what not. Just say you think you've gotten a better deal at your bank and leave it at that.
As Trek says, he hasn't lost out on $ just on a little time. This is standard in the industry. Many (smart) people shop their loans. Often people apply with a 2-3 brokers/lenders and "float" the loan (not lock in a rate) until one of the lenders offers a better rate. Until the moment of lock, lenders and brokers both have invested time and maybe some money (credit, maybe some pre-underwriting and number work ups).
In the mortgage industry, they are used to loss in the pipeline. It's just part of the game.
Anyway, don't feel bad. He was going to make a lot of $ off of you. And don't let him bully you or make you feel bad. He was going to make a lot of money off of you.
<yeah.. the surprise thing sounds like a load of bullcrap. If you were going to be credited for any $, it should be disclosed in the GFE. As we say in the industry, "RED FLAG alert".>
Push the pedal down watch the world around fly by us