My partner is the one with the problem, but isn't the one asking for advice

I'm in a V with a man and his wife, and while my metamour (the wife) has gotten through many of her issues surrounding abandonment and jealousy and really welcomed me into their relationship, my partner has started feeling jealous about her seeing another man. He wants logically for them to be together and explore their feelings like he and I have, but he's struggling with feeling jealous when he sees them together. Do you have any advice for him on how to manage that?

It doesn’t matter what advice I’d have for him, because he’s not asking me for advice. You can’t manage his feelings for him, and you can’t seek advice for him. I don’t give unsolicited advice, and I don’t advise you to try and act as a go-between to try and give it to him.

It’s not a healthy relationship dynamic that you are doing this work on his behalf. Please do some thinking about the expectations in your relationship and reconsider how much you are doing to manage and mitigate his feelings. If you’ve taken it upon yourself without signals from him that he wants you to, then drop it. If he’s asked you, implicitly or explicitly, to do this work, start refusing.