He is with her, and they know that I know (5)
We think this is at the heart of what jealousy is all about. It's not just that "he is with her" and that you've been dumped. It's that they know how bad it makes you feel. That's what really makes it ache, that feeling that they are doing all this just to hurt you, or to humiliate you.
While they laugh, laugh at me, at me fled to the drear (7)
This is what's really driving our speaker. She feels like she's being made fun of, that her former lover and his new girlfriend are laughing at her. Maybe this is where she starts to step over the line too, from the kind of jealousy that anyone might feel, to something a little bit weirder. Honestly, we think she sounds a little paranoid here, a little obsessed with her own imagination about what's going on.
What a drop! She's not little, no minion like me— (29)
Okay, now she's just being a jerk. It's hidden by all the poetic language, but basically she's saying this new girl is fat. That's jealousy talking, for sure. But come on, be honest. Maybe you've been through a bad breakup, and maybe you found yourself crying into your second pint of ice cream, and maybe you've let something like that slip out. Not that we'd know anything about breakups, or crying, or ice cream…