I think it's about him and/or his girlfriend being high on heroine. "it feel good, girl, it feels good." "Then feel your weight in arms I'd never use" may refer to his girlfriend shooting up but he would never do it himself. "See the way you hold yourself Reel against Your body's borders" is the feeling she gets when she is high, which is very common for a high on opiates and/or other drugs, to feel like you are not in your own skin or need to get out of it.
I think it's about him and/or his girlfriend being high on heroine. "it feel good, girl, it feels good." "Then feel your weight in arms I'd never use" may refer to his girlfriend shooting up but he would never do it himself. "See the way you hold yourself Reel against Your body's borders" is the feeling she gets when she is high, which is very common for a high on opiates and/or other drugs, to feel like you are not in your own skin or need to get out of it.