So I'm looking for a middle eastern (actually it might not be...) yaoi manga, where this rich guy (he might have been a prince) forces the brother of his former lover to take his place as his lover. And so the guy is forced to live in the palace with him and there's this servant who's tasked with taking care of him but he doesn't like him because the servant has an unrequited love for the prince/rich guy.

Anyway there's this one scene where the captive guy breaks a glass plate and holds a shard up to his throat and says something like "I don't want you to look at me and see that other guy!" or something like that.

It's not Garasu no Suna/Sand of Glass.

There's no I in TEAM but there's a U in SUCK

Honoo no Suna?

hoshika got it right on the money. It's definitely Honoo no Suna by Tamaquis Wren. She has a couple of other yaoi titles that have a Middle Eastern setting too.

Yess! That's the one! Thanks so much!

There's no I in TEAM but there's a U in SUCK