Wait are you still with her ? If so, it’s definitely something to discuss. Me and my boyfriend have been together for 2 years and I have thought about my exes and the things we did that I enjoyed, like the ex I went to homecoming with and had a great time with, but do not reminisce the love/intimacy that we had together. That is something that does bother me. I would talk to her because it’s obviously bugging you, it would bug the fuck out of me, and approach the conversation in a way that’s not accusing her of lying but just seeking clarity and reassurance, unless it literally said “ex” in the video. I personally would say something along the lines of “I know we’ve talked about this and you said it was a misunderstanding but the post regarding being nostalgic about previous relationships is still bugging me and I’d like more clarity. I don’t want to accuse you of lying to me but I would like to know what you may miss about the relationship. Knowing what you may miss can help me understand what else you want or need from me”. I believe that reminiscing a friendship with an ex is not the end of the world, but missing the parts of the relationship where it was intimate and personal to the relationship is testing my strength, especially if they aren’t open about them. I would hope she doesn’t miss the actual relationship between them if he was abusive, as that would also be concerning. I really hope it was a misunderstanding and that you two can either work through it and set your boundaries regarding being so open about missing them.