Welcome to our forum.
I just think polyamory is very different from what we are trained to expect, so it's natural and very reasonable to have some disoriented (even queasy) feelings about it at first.
I don't think Blu will leave you because of Bent. Sure, she's been monogamous in the past, but I think she can see now that loving more than one person is possible. I know I can't guarantee it, but for what it's worth my impression is that she'll stick with you (as well as possibly with Bent).
In any case, monogamy wasn't working for you, as you said, so I think you're taking the right pathway here.
It's good to have you on board; hope we can be of help with any questions or concerns you have.
Love means never having to say, "Put down that meat cleaver!"