Jonathan says: Let him know.
I totally get that Jake’s going through a lot and that stinks, but it doesn’t seem reasonable for you to suffer too. Because you’re his best friend, I think it’s your responsibility to be honest with him.
If Jake’s behavior toward you has been unkind or disrespectful, chances are he’s acting the same way with other people too—and he might be completely unaware of it.
If he continues acting this way, he might end up pushing away the people who care about him the most, like his best friend. By letting him know how his negativity is affecting you, you’ll actually be helping him.
When you speak up, you don’t have to say “You’re being a jerk.” Instead, you can say something like “You don’t seem like yourself lately. Can I help?” That way, he’ll understand that you’ve noticed his behavior—and you’re being a supportive friend.