I know of several cases in real life, where a Dom has several subs, but the subs are exclusive with him. All parties want it that way. In that case, it is ok.

It would not work for me as I am jealous in a relationship, though.

However, if the "Dom" in question tries to tell you
- this is normal / everybody does it that way
- you have no right to oppose that
- if you oppose it, you are not a genuine sub,

BURN THE HOUSE!

As I already said elsewhere, what is OK in a relationship is ONLY to be decided by the partners involved, NEVER by anyone else.
BOTH (or all) partners, though. Always. Never by the Dom alone.

What still escapes me is: What sort of Dom would want an unhappy sub?
Or, what sort of sub would want to be with a Dom who does not give a fuck about her emotional well-being?