you will probably need to have the landlord or mgt company issue you a new check, with only the 2 names on it.......you can ask a bank teller if a copy of the ID from the 3rd person will be good enough to cash the check
You may want to contact the apartment people and see if they'll cut you a new check with just you and your fiancé's name on it. It will surprisingly be the easiest thing to do.
Have a replacement check issued in one name, cash it and divvy up the funds
Go back to the person who wrote the check and explain the situation. Maybe they will tear up the old check and make out a new one for your part of the money to you, and simplify things.
Why not ask your bank the easiest way to resolve? They wont accept as you could have forged that name. They might allow you to deposit the check though, have you tried that?
A notarized release might work, in what country is that roommate now?
It's up to the bank. WE can't tell you what they'll accept.
You'll need to talk to someone at your bank and find out what you need to do.