If you are in a relationship with someone and they openly talk to someone you don’t get along with..

Not everyone likes the same people. Just because one gets along with someone doesn't mean you will or just like you may get along with someone they don't. It is hard being an adult sometimes lol true. But at end of the day. Pick your battles. I mean if you trust this person and you know its just friends. Then best probably to let it go

Being bitter. But being bitter inside and pretending everything's okay on the outside is not great either. So the best thing is to acknowledge bitterness and depending on the length of the relationship, express the fact in a non commanding or non suggestive way.

That is just you trying to control someone else's feelings and actions.
Maybe if it were me I would ask them why they think that person is worth socializing with.

I will never ask a partner to stop talking to someone. I will let them know who I feel about that person. At the end of the day, maybe I’m the dick.

I think it's reasonable to find out why your S/O is doing talking with that person, esp. because your S/O might be both misguided & being played.

You have to tolerate it.

Hold clay in your hand, tighten your hand and observe the duration for which it stays there.

You will get your own answers.

Maybe not ask them not to talk to them. Ask them to talk about it instead, that will help you both

Then u have every right to ask them not to talk with them IMO. Always be open and honest abt ur feelings.

Just let it go.... unless its like a full on enemy otherwise not a big deal

You being bitter.

I have done it before.

Bitter