Testify Be Common

had her man's back - he was facing years

to "get someone's back" means to protect, speak up for, or support them. he can't convince the court of his innocence on his own, so he needs his woman to testify on his behalf as he faces a jail sentence of several years.
man's back is in reference to being on his side/supporting him... facing years refers to the possibility of jail time i.e. she supported him even though he might be going to jail for many years~