If you are happy together but busy, why suggest adding others even though your partner doesn't want that?

He may want the same permission

It really depends on what his beliefs are about monogamy and relationships in general.
Either he is not all that invested in the relationship if he is a monogamist or he sees nothing wrong in open relationships if those are his beliefs.

He is cheating lol. If my partner suggested something like that in a serious manner then I'm out.

He has possibly lost interest in the person or wants permission to be intimate with someone else, but first wants to see the persons reaction or if they would agree to it themself, or he has already begun doing it.

I think one can develop tastes for things. If two people in a relationship can develop in a roughly similar direction, it might improve their quality of life. No hard and fast rule. I don't think that's quite what you're asking though.

He’s wanting you to be ok with him doing it

I don't understand the busy part. If he is too busy to spend time with you, how can he find the time to spend with someone else?

It's a decision for both of you to make. Personally I wouldn't suggest something like that if my partner didn't bring it up first.

it has been known to make the faithful man's sperm more competitive FYI

He is too "Busy?"

Then he is just not that "into you".

Repeat after me...... NEXT!

Well, he doesn’t think you’re busy.

That means that HE wants others and he is trying to be slick about it so it will seem like it was for his partner that he suggested bringing in outside people.

Me personally unless my husband is totally jealous of someone else sharing me then I don't want him.

Break up time.

If the guy knew me well and cared.... he'd never suggest such a thing.
From what I know.... that type is usually looking at others already and wishes to have the "partner" make it an agreeable deal.

Then time to part ways for me then