I (41f) have been dating birch (39m) for a year.

We have had a beautiful relationship. We’ve had some ups and downs from how we date as poly people. Nothing earth shattering but there are times when there are more discussions then we’d both probably like. I’m his first poly relationship. We spend 3 to four days a week together and we call each other our “person” because we’ve decided to be more interdependently involved (holidays, being each others emergency contact, first calls if something happens, responsibilities with each others families). We don’t live together and don’t plan to. We both date others which takes another day or two out of our week but everything balances out to how we both like our deal.

Birch is head over heels for cedar (31f) that he’s been seeing for 3 months. NRE is strong. Cedar used to live here but is now doing travel health work. They talk on the phone. Cedar has visited here and birch is going to visit them for five days next month. He’s very excited and I love that for him. Here comes the part I need advice on.

Cedar is moving back to town at the end of August. Not for my partner, just wants to be back in their city. This immediately brought up a fear response for me. I don’t know how things are going to be when cedar is back in town. I keep having thoughts of birch wanting to spend all their time with cedar. I’ve talked to birch about it and he has said “that’s months away.. what’s the use in worrying about it now” which doesn’t really tell me anything about his intentions. I’m more of anxious over thinker and I can’t get it out of my head that he’s going to cut our time to be with her. Cedar is not dating anyone else currently (they are poly, just ended what they called their primary partnership) and I’m afraid that my partner will be their sole focus.

Is there anything I can do to mentally prepare for this? Anything that we can do as a couple that we should talk about? I just want some advice on how to handle this fear and what to prepare myself for.

TLDR: partners other partner is moving back to town and I don’t know how to handle the fear involved in that