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

Although it may seem like a good idea to you, and actually others as well. Your s/o could be rubbed the wrong way, and take your complaint in a controlling/demanding way. I suggest explaining how you feel about them being in contact with their ex. If they still continue to do so, unfortunately there's not that much you can do other than accept. There's a foundation of trust supposedly in a relationship, and if you trust that your partner won't act on anything or have romantic relations with their ex, then it'll become more and more bearable.

if there is a reasonable explanation to it, yes. try just sitting them down and telling them. be calm, and show your persepctive but make sure to keep theirs in mind as well

If an interaction seems to make you feel uncomfortable between your partner and his friends or ex you should definitely communicate it to him. Make him/her understand that this is bothering you and list all the reasons why it does for example (I don't like it when she/he says this …. or does this....). If they do not respect your wishes, express that to him/her. Set boundaries for yourself, all in all, being in a relationship it's about being able to build trust within one another. If you cannot trust him, how can he trust you if you were in his shoes.

You can ask your significant other, if it bothers you then you should. Because it may cause problems in the future between you two. And you can ask then by confronting them about it. Tell them honestly what bothers you and why it bothers you. That'd be the best way to ask them to stop talking to their ex.

Here's the thing about that - Your significant other is someone that you have a relationship with, but you do not own them. If you are uncomfortable with it, absolutely voice your feelings of insecurity to your partner if you so wish, but realize that you do not have the right or the power to tell them who to associate with or speak to. There's an very toxic mindset floating around, that people start to treat others like they are property to be managed - Which is not right, valid or fair. It's a fairly abusive pattern, to be honest with you. But if you feel so strongly, I would lead a conversation of "I statements" to address your concern with to your partner.

I believe no one should be restricted to contact their ex, as ending a previous relationship does not mean removing them from your life. You can try communicate with your significant others about your worries. Let them know that it is a disturbing thoughts that you wish not to worry so they won't be agitated. Communicate with them how to work things out and how to alleviate the worry. First of all, both have to be comfortable on talking this uncomfortable topic. Set some guidelines before starting the conversation, because you deserve to be heard too. On the other hand, you should listen to your significant other.

I think trust is really important when it comes to relationships. It is important you set boundaries and let him know how you feel when it comes to his actions. Forcing him to stop talking to someone because you feel uncomfortable may be slightly unreasonable on your part, but if he were to continue if you talked to him about this matter, you need to set it straight with him and not hide it. Like I said before, trust is important and you two need to be honest towards each other. Once the trust is broken, it will be hard to fix it. Just like how you can't fix a broken bowl back to it original form.

Perhaps it's more important to consider what about this might be important to you. Are there global issues relating to trust, or is this specific to a particular ex? Either way, an open dialogue with your partner is likely to be the most constructive means of addressing this. Ultimately, your partner is more likely to respond positively to a conversation around feelings and experiences, rather than being simply asked to stop interacting with an ex. At first, the conversation might be difficult and make one, or both, of you uneasy. However, this is one of those really important conversations to have, and will likely result in your relationship being strengthened.

No you should not. It may be a way in which your significant other is dealing with the break up at the beginning. Also they might have broke up on good terms and now are friends. If you start to tell them to stop taking to each other your significant other might feel like you do not care about what they need and are trying to control them. This in turn can lead to arguments and issues between the two of you. Which could lead to you breaking up with your significant other just because you are talking to your ex.

Depends. Just make sure not to project your insecurities on to them.