No one should ever have a problem with two or more CONSENSUAL adults being in any kind of relationship.
If it is non consensual then there is a problem!
If it is abusive then there is a problem!
If you feel unsafe with your partner(s) that is never okay!
Relationships come in all different shades and should all be equally valid! But abuse is never okay! And I mean any form of abuse.
I am for consensual adults having the freedom to love whomever they want so long as they too are a consensual adult!