Having a loving relationship with more than one person would probably be considered polyamory.
Having a *sexual* relationship with more than one person without love being a factor would probably *not* be considered polyamory.
Having a relationship in which two people are required to do something because the third wants them to, and which has only formed because of what the third person wants, would probably not be considered a loving relationship.
It sounds like your boyfriend is willing to give you a lot, and from your post, it sounds like you want even more from him and from your potential girlfriend. Does your boyfriend want to have a threesome with you and this girlfriend? Is that your reason for forming the relationship? Or is that your fantasy and he's going along with it?
If you're serious about wanting to have a *relationship* in this manner, you might need to do some prioritizing and compromising. If you find a woman you care about deeply and want to have dates and sex with, but she isn't willing to consider a threesome with you and your boyfriend, is that a deal breaker? If you only like her as a friend, but she *is* willing to do threesomes, can you deal with not having a love relationship but just a friends-with-benefits type? If you and she are in love with each other but she and your boyfriend just kind of tolerate one another, would you be okay with that?
Try figuring your *primary* reason for wanting to do this. What is your one hundred percent absolute hard limit? If you go into this with several set expectations and are unwilling to compromise or negotiate on ANY of them, you're setting yourself up for failure. If you're willing to compromise on at least some of what you want, you might have better luck.
As my Hubby would put it, this is a THREE-yes system. You aren't the only one involved, therefore your wants, wishes, and desires aren't the only ones that matter.
Me: 44, cis-het female, poly
Hubby: my husband, 42, monogamous
S2: my "attachment", male, 44, undetermined
Best Friend: male, 38, platonic; the one who keeps me sane through all this!
My daughters: Alt (age 19) and Country (age 16)
S2's sons: Spikes (age 9) and Beads (age 6)