I think that when you've gotten to the point with someone that you consider them like unto a marriage partner, it's worth taking a minute to check in with them and see how they feel.
The terms are irrelevant, but I think it's usually good to make sure every now and them that you're on the same page... it could mean the world to him to hear it if he doesn't already realize you're thinking this way, or it could bring up something you two really need to discuss if he's *not* thinking in the same terms.
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.