I've been there occasionally. Once in a while I'm still there, but I think I didn't use those types of terms much to start with. I'm more emotional than MC, but more logical and analytical than TGIB, so when it comes up there's no one way I handle it. Ultimately, though, I fall back on TALKING about it. (So, yes, you should probably check-in with your partner and see if he's noticed your language change and what he thinks about it.)
TGIB will playfully use the term, "Mine!" It makes me smile, but at one point I asked what his thought process was behind saying that. I wanted to make sure he knew that, while I WAS his, I wasn't ONLY his. The key, imo, is to not immediately try talking about it in the moment, but try to accept it graciously and then a little while later say, "Hey, remember when you said X?" and go from there. If it something makes you uncomfortable because you don't know how to respond, tell him so! You can even ask, "Since I'm not okay with responding *this way*, what's another way you would like me to respond so you know how much I love you?"
I think overall our society puts too much emphasis on being the best/most at anything. An adult's "I love you most!" really isn't any better than a 4th grader's "SHE'S my best friend, not you." I don't think anyone has to be the MOST or the BEST in relationships, which is probably why I usually had a group of close friends rather than a best friend, and why I rarely use those kinds of terms to start with.
Good luck with figuring out your new V!
Pan Female, Hinge in a V between my mono (straight) husband, Monochrome and my poly (pan) partner, ThatGuyInBlack