For heaven's sakes, Buttons, don't put yourself, your family and your other animals at risk! Don't let your kind heart win out over your good sense. There may be a rabies hotline you can call . . . I know there is one here.
If not, call animal control, explain that you have caught a young rat that may have rabies, ask for it to be euthanized and tested. The brain must be intact for them to test it.
This kind of situation is exactly why we have our dogs and cats immunized against rabies--we never know if and where an infected animal may show up. Insist that you get the results of the rabies test.
There is treatment for exposure to rabies and if you or your boyfriend has been bitten, scratched, or has any open wound that may have had contact with the rat. My brother had to have it a few years ago when he was bitten by cat that had not been immunized. Three needles in the arm was all. Better safe than sorry.