If I were you, next time they're both in the same room with you (which won't be an issue since you say she's constantly vbutting in on your dates), just say the following right out of the blue with no warning:
"Look B, I'd love to help you out with my truck, but you need to help me out by letting P and me have our quality time without you."
After you say this line, wait for a response, and take it from there. You should be good to go.
The situation is hopeless, but not serious.
Reality is too complex to be spread all over the world.