Prison: Bailbondsman/Defendant Already Sentenced

My question involves criminal law for the state of: Ohio. I recently consigned on a $10,000 bond through a bail bondsman. Originally I was told I never made it on the Bond due to my credit score. But in reality, myself along with 2 other cosigners are on there. Anyways the defendant paid $2500 fee to bail bondsman in Jan. He never skipped court however he never paid the $6500 he owed to bail bondsman. He recently lost his case and has been sentenced. He is waiting transfer to prison. The other day the bail bondsman contacted me because they couldn't locate defendant. I told them he was in jail. Then I asked was everything ok with his bond and she informed he never paid. She told me all : of us were equally responsible to pay. So I called her the next day to set up arrangements and she then told me only I was responsible to pay. So I'm supposed to go sign a promissory note agreeing to pay $100 a month for 65 months but friends of mine are saying to get another opinion before I go. Do I in fact owe the $6500 or does he?

Prison: Bailbondsman/Defendant Already Sentenced