Can or should I ask my significant other to stop talking and to not associate with his ex? If so, how?

You cant stop anyone from talking to anyone else ? They can be friends but nothing more ask him the relation ship between the 2

The best thing to do is open up to him about your feelings, let him know what is on your mind. Try to talk calmly and let him now that what he does is making you upset, and that you care about the health of your relationship with him.

I would start by talking with you SO, and explaining why it bothers you. I would not try and make demands! This comes off as controlling, and many times turns out much different than you had hoped!

Learned how to recommend a person to someone who spoke his language, which i feel is a great thing to know how to do :)

It depends on how sincere or romantic it is. Is he talking to them because of school, work, formal things? Or is he taking time to talk to them about general stuff, funny stuff, etc? You do have the right to say you don't feel comfortable with him talking to them too much. You don't have to tell him to stop talking to her unless you suspect cheating. This suspicion can't let you stop him from talking to them, though. If you have a suspicion, you need to ask. I think you two should talk about this face to face, until you two figure it out. I hope you do

I don't think you should ask them to, because a relationship should be based on trust. If you don't trust them to be faithful to you (if that's what you're concerned about), then probably the two of you are doing it wrong. On the other hand, they shouldn't misuse your trust as well, and know the boundaries of what they can or cannot do with his ex. I think it's all about trust.

My first suggestion would be to look at what you are afraid of about them contacting each other. If you can identify specific fears and communicate them to your partner in a way that does not accuse him i.e. express your fears as 'I feel afraid that....' and let him hear your concerns so that he can have the chance to see your point of view and let him respond to you. Then you will be in a better place to explore this question further

If it's something you strongly feel about you should be honest but also be tactful. Simply saying that you're unhappy with him talking to his ex should be effective enough.

If the ex isn’t disturbing/harming your current relationship, then it is best to leave things as is.

First you should figure out why this subject disturbs you so much. Are you afraid of loosing your partner? You think you are not good enough? I think when you are in a healthy relationship and are not afraid of missing the partner or jealous about previous relationship, you don’t mind hearing about the ex. On the other hand, maybe the problem is that your partner is obsessed with the ex, and exaggerates talking about them, then I think you should tell him/her and try to find a solution for him to get over it.