As much as Leon hates to say it, there is a certain hierarchy to his romantic life. His spouses take precedence in all things; if they need him, he puts whatever he's doing on hold. If he needs them, he knows without a doubt they would respond in kind. If they didn't get along with someone he was considering a commitment toward, he would have to let that person down gently. (If they ordered him to do this, it would be a different matter, because that's unfair; he discusses it with them before it becomes an issue, like adults ought.) As he explained it most recently to Valarin, his spouses are the ones he will always, at the end, come back to. He knows them as deeply as they can be known, and vice versa. He keeps as few secrets from them as he possibly can. They can bully him for his own good, and he can bully them back. They are the ones he puts all his faith in, that make him feel at home, safe, and normal. They are home for him. That's why they go on his collar; it's his last remaining piece of home, and they belong there.
Asking him to label anyone else would get a wierd look. If he had to use any particular term for it, the ones who are not his spouses that he chooses to spend most of his time with, harbors meaningful feelings for, and trusts deeply would be loved ones (this includes the ones he doesn't have sex with). They could become spouses, maybe, eventually, but they don't have to, and most of them won't. There is no spoken commitment, there are no promises, they're just where they're at. Leon has had loved ones who just up and disappeared on him one day; there was no commitment between them, so he wasn't angry about it from that angle, but it did sting to lose them. Until their initial ends up on his collar, they are very close friends and there are no expectations. There's a little bit of room for bullying, but it's a lot more cautious and he's more likely to let their business remain their business. Examples include but are not limited to Safrona, Cay, and Celedyn.
And then there's everyone else. *shrug* Leon considers sex just another activity people can engage in together, like playing a sport or seeing a show, not a connection or a milestone. He's said for years that it is infinitely easier for him to share his body than his mind or his heart; sex does not instill within him a sense of obligation, and he will make absolutely certain a new person knows that before he's willing to get with them. If you want to love him or be loved by him, talk with him and share things with him. The difference is what you share and what you promise.