N & J, if you're browsing this subreddit, stop reading. This is C, and I would overwhelmingly prefer that my post asking for insight does not become an issue brought up 'against me' or something.

Title is short version, but I imagine you can get the gist of it from that.

My partner of 3 years(plus an additional 7 years of on and off history prior to that)has recently started seeing a mutual friend of ours. The situation caught them both off-guard(he was in a relationship in which he felt deeply neglected, he left it immediately after he realized his feelings for my partner), but I saw it coming several months ago just from witnessing their interactions. I never said anything to either of them because I knew making either of them acknowledge it would have ruined things as their nerves would have interfered in the natural progression of their relationship.

It's been going on for 3 weeks now, and I am struggling with feelings of being neglected. I understand NRE(New Relationship Energy)can play a large role, but she's been having lengthy visits with him 3-4x a week and aside from brief walks or grocery runs together, I'll only get to spend time with her once a week. It's started impacting our sex life as well, because I'm struggling with feelings of inadequacy and it's interfered in my ability to 'stay up' when the intrusive thoughts enter my head.

Not helping matters is that when they're together, out of a sense of courtesy, I reduce my messaging/texting to both of them to a bare minimum to avoid feeling like I'm intruding, but she's consistently texting him while we're together. I've brought it up with her and she just keeps brushing it off as NRE and it'll wear off "eventually" once the 'novelty' dies down.

For his part, the mutual friend has never been involved in polyamory before and he's still somewhat on the fence on whether polyamory is truly for him, so this burgeoning relationship is a sort of 'test run' for him in some ways. To me, it just feels like they are both throwing themselves headlong into this, while her and I have previously discussed the need to move new relationships at a gradual pace so all parties have a chance to adjust to the changing situations.

I've been asked not to bring up too many of my concerns with him so as to avoid scaring him off(he is trying to be very mindful of my feelings and does not wish to jeopardize our friendship or my relationship), but I also just feel like whenever I bring them up to her I just get brushed off with the NRE explanation.

So I guess my question is, is waiting out the NRE my only viable approach? Is there anything I could be doing better? Please ask questions if you want clarification on anything, I just sort of feel like I'm spinning my wheels here.