For some of us saying the "L"-word is a big deal...for others not so much.
(You can read my post the first time I said it to my boyfriend HERE
The question is - what does this mean to you, your boyfriend, and your husband? Only those involved know the dynamic.
When you and your husband were discussing polyamory - what agreements did you two come to about what/how much of your relationship with another partner was expected to be disclosed? Is your new partner aware of these expectations?
In our particular arrangement, the possibility for new loves developing is why our arrangement works - it's kind of the point. However, there is the expectation that as things "develop" we talk about them and each individual's (EACH individual - old partners, new partners, metamours, etc.) concerns and comfort levels. In addition to being partners and lovers we are all friends. If I was developing a relationship with someone and emotions were getting deeper, that is certainly something that I would share/talk about with a close friend - so, of course, I would talk about it with my husband and my boyfriend.
Your situation may be different.