Divorce nostalgia

So I found out my Ex-Husband has a new girlfriend today through mutual friends. We ended not so great at first, but since then things have worked out amicably and we nod and smile and are cordial in public. I feel a mix of emotions right now. We've been split almost 2 years. I'm in a really healthy and happy relationship myself and I feel really happy for him I think there's a feeling of Oh okay he's actually moving on that makes me kinda sad though too. Knowing now she gets to know his family and life and be apart of their world. Maybe that makes me foolish or pathetic. Just wondering if anyone else had that too