He didn't get it because 3-4 years ago when he applied for a visitor visa, I had my parents write a letter of invitation inviting him to come visit. He was denied that visa and they asked about it again today, shortly after which he was denied as well.
I fucked up everything with that letter. I thought it would help...
Such a shame this happened, but don't give up! There are still options and there are still chances he'll get it next time. Take a breather and then see how you two can approach it from here. Rooting for you!
It's totally insane that the letter was the reason he didn't get the visa.