Dear Annalisa

My ex and I split up five years ago. We have a 10-year-old daughter. Although the separation was difficult, we have always communicated in a friendly, positive manner, reached co-parenting decisions together, and rarely had any disagreements over raising our child. We have split holidays equally, have met at important dates such as our birthdays, and have had dinner together once a week for a couple of hours.

Eight months ago, my ex met someone new and I was happy for him. Initially, his girlfriend was reluctant to have a relationship with someone with a child. She has now begun to make demands on my ex in relation to our time together as a family. She refuses to meet me, has asked him to have lunch with me and our daughter only on our child’s birthday, and has now asked him to stop spending any time with us if I am going to be there. She won’t agree to any other arrangement, such as us meeting once a month for lunch.

I have been very upset. I feel powerless. I have step-by-step been told what is going to happen with no possible negotiation. He is going to tell our daughter about the changes to our arrangements in the next month and I am really worried about what this means for her. Also, the girlfriend is moving in with my ex, and my daughter will spend a lot of time with them and I feel really nervous and anxious, given her animosity towards me. I have no idea what type of person she is, how she will be with my child, and what sort of home they will create for her.

I feel I should be able to meet them before they move in together to discuss the needs of our daughter and try to work together for her. What can I do?

The first thing I picked up about your letter was your anxiety, but also how much you – and the new girlfriend – want to control things. I totally get that you must feel (rightly) angsty about who your daughter comes into contact with, but she will be with her father. Don’t you trust him?

I contacted psychotherapist Jenny Dew, who specialises in therapy between couples (bacp.co.uk) and that was the first thing she said, too: “There’s an awful lot of control going on. Your ex-husband seems to be quite passive. I’m also wondering if you are struggling with the ending of this relationship with him.”

It is great to have a good relationship with your ex, especially when there are children involved. But it really is up to your ex to manage his time with his girlfriend so that his daughter is included appropriately. Dew also wonders how much you trust your ex-partner: “Do you trust him? Because, if so, one would imagine he would be equally concerned about your daughter.” Dew wonders if you are worried about being replaced as a mother? This is normal, but I think if you can step back a bit and focus on exactly what it is you are really worried about, you may be able to work on that. After all, you say that you have nearly always agreed on issues to do with your daughter.

Sometimes when couples split, they forge a new semi-relationship where they are still involved, but are not “together”. This works until one of them moves on. I think, if you are honest with yourself, this is what has happened.

Dew completely understands how the thought of his girlfriend wanting no contact could feel threatening, but suggests you talk to your husband so that you can find a solution together, with regard to your daughter; perhaps you could start by asking him how you could introduce these changes to your child.

Dew also suggests trying to “defuse the situation. When one is caught up in the emotion, it is sometimes difficult to make rational decisions. Just because you have a fear, it doesn’t mean anything is going to happen. The new girlfriend may feel threatened herself.” Both Dew and I can see that dinner once a week for a couple of hours might seem excessive to a new girlfriend.

Your top priority, of course, is your daughter, but, hopefully, this is a priority for you and your husband. Also, she is 10. She will, as Dew says, “work it out for herself pretty fast”.

It is important this new woman isn’t presented as a threat or someone scary. Be neutral. That way, your daughter will feel she can come to you if anything isn’t quite right. Just because the new woman doesn’t like the sound of you, does not mean she will be horrible to your child – the opposite might happen, which I realise may bring worries of its own. And, as I really must stress, your daughter will be with her father.

This article first appeared in The Guardian Family section on 11 September 2015.