The first, and hopefully only, address should come from your love. They were the ones in the relationship and dealing with this person and it is best to have them confront them. Not only does this ease the possible tension, but it can provide closure and a sense of true termination of the relationship. Your partner should stand up and stop any form of disrespect that has transpired whether it is constant or inappropriate calls, social media comments and postings, the whole grapevine rumors thing or anything that is making your new relationship suffer or puts it in jeopardy of ending.
If nothing is resolved from the two exes speaking, then we may need an adult sit down between the old and the new. While it can be so tempting to meet up, or converse, with this person and just put them in their place, this is not the way to go. It will be best if you guys sit down and you show that you sympathize and understand their stand point, but at the same time address what is and not acceptable. If that means that there will be no relationship at all between the two exes, then that’s what needs to be stated and provide a reason why. Do you need to explain or provide any reasons to this person? No, not at all. By providing this explanation, will it change the outcome? It very well may. What this does is gets THEM to understand and sympathize with you. You can put them in your shoes for a bit. Don’t say anything that gives them leeway. Don’t say “this makes me feel uncomfortable,” “this is putting a strain in our relationship,” or anything else that may insinuate that the relationship will end and they can shoot their shot. Instead, address how it is inappropriate for the relationship, not acceptable and unappreciated. Flip the tables and put them in your shoes. Exhibit confidence and make it known that you will not be disrespected.
If children are in the mix, I feel for you. Only because this means that this ex has to be in the picture for AT LEAST 18 years. In this instance, all three of you guys have to try your best to get along, set guidelines for the relationship as far as when to contact one another and what to contact one another about, what is expected from one another, what is appropriate or not, and not using the children as pawns, and have an open line of communication. I’m sure that feeling replaced as a parent is a horrible feeling, so the attempt is to eliminate that feeling while establishing your role in the children and their parent’s life. This situation should be able to be addressed between the exes as well, but a sit down with all three is a great way to show support for one another and display how serious, not only your relationship, but this situation is.