Help, please!

I have been seeing someone for about 8 months now. It’s my first poly relationship and there have been real struggles (for both of us, I guess). The woman I’m seeing already has a partner and the two of them see each other about once a week, on average.

From the beginning, I was clear about needing some time between her seeing her other partners (she had more when we started dating) and her seeing me.

I never said, “you can’t see this person on Friday night/ Saturday and then me on Saturday night” but more like - “I think I’d feel really weird about it so perhaps we could see each other on the Sunday instead”. She seemed to get that and we haven’t had any issues about it before.

Now her other partner who was supposed to be moving cities this month has announced she’ll be working part of the week in this city and part of the week elsewhere. She’s also asked to stay with our mutual partner when she is in town. The problem is that the nights she has asked for - are the nights I would usually stay over. My gf agreed and then told me after the fact. I was pretty hurt she a) agreed this whole change without involving me in any way and b) cut into our time without any discussion.

Where does my need for space between partners come from? I think it’s because I had a really shitty first relationship in which I was constantly being snuck in and out of my gf’s home (she was cheating on her husband with me) and it always felt wrong and made me feel dirty. I explained this to my gf but the response was very much “this situation is different.” Which it is. She also said she discussed it with a friend who’d said “that sounds like her (ie my) problem” which I found hurtful and dismissive.

Another thing she mentioned is that no one else that she knows needs time between partners, though it seems clear to me (after searching online) that it’s a common source of discomfort.

So my question is - is it fair that she has made these changes and expects me to fall in line with them despite how uncomfortable I feel either lying in her bed or getting out of it knowing that someone else was/ will be in it very soon after?

I understand these are difficult emotions and that maybe it would help to do some work around it but I don’t even know where to begin... does anyone have any ideas?

I’ve done the jealousy workbook and read polysecure but no dice. So far anyway.