Need an unbiased opinion

Two people broke up & decided to work things out. One of them wants to be able to talk to their EX while this couple is trying to get back together. This ex has already caused problems in the relationship previously with trust issues. One partner has expressed that they feel that this will be detrimental to the relationship and cause trust issues and will only impede the process of trying to repair the relationship and cause hurt. The other is insisting that they have to talk to them for their Mental health & claims it is completely platonic and claims that they will break it off afterwards. The X does not even know that they are getting back together, and the person will not offer immediate proof that it is platonic and this person is not trying to interfere with their getting back together. They want a couple days in order to do that, claiming that the other person is trying to rush them. Do you think it is an unreasonable request to be able to talk to an ex during this situation while refusing to offer immediate proof that it is platonic and beneficial to the relationship?

I understand that but do you think that it is an unreasonable request to be able to talk to their EX while trying to patch things up?