TLDR: partner has a primary nesting partner. She’s encouraged me to date but when I go on one she gets cold and distant for several days.

Looking for some advice. My partner and I have been together for 3 years. She met me and her primary in the same city around the same time. She’s poly and we were both fine with it. They practiced dating the whole time but I wasn’t really interested until recently. That’s because they moved across the country together. I really want to maintain our relationship, it means a lot to me. She encouraged me to get my needs met while we still see eachother roughly once a month.

Here’s the issue. I’ve been on a couple dates. I let her know beforehand. She seems ok, wishes me a good time, etc. However, she then gets cold and distant for several days. She reads every interaction I have as if I’m leaving her. She’ll stop chatting with me like normal. Bottom line is it sucks and makes me not want to date at all. She knows she’s struggling with it. She’s admitted it’s her insecurities and we eventually get back to a good place but it throws me for a loop. I feel like I can’t do anything right during that time. It triggers the people pleaser in me who wants to soothe her feelings but they’re hers to deal with.

So I’m looking for advice on how best to support her through her turmoil without just throwing in the towel. I’ve told her I give up dating but she insists I shouldn’t. I feel like it’s important I be able to be strong in the face of her feelings I’m just not sure how to present that. How do I let her know I care when she’s pushing me away?

Thanks