Aaron Hernandez is playing matchmaker behind bars ... 'cause he's been letting his sexually deprived prison buddies respond to his female fan mail, TMZ Sports has learned.
One of the lucky gals who wrote to Aaron got two responses last week -- but neither of them were from the ex-Patriot/alleged murderer ... instead, she heard back from some of his "roommates."
A guy named "Rondo" and a dude named "John" -- who are both locked up in the same prison with Aaron-- say that AH encouraged them to write her ... and suggested she look them up on FaceBook.
Rondo writes: "AH is my cellmate and friend he had given me your address saying he has a good feeling about you and I becoming penpals."
He then added "I'm currently in prison for beating up a cop. So tell me about yourself."
"John" writes: "Aaron said that he hopes you can write back, and if you do since you'll know what we look like send a picture so we can see what you look like. If you don't mind."
As romantic and heartfelt as their letters were ... we're told they did not receive responses.