Felt so weak today

It's been an year since I left her. She hurted me in ways that I could have never even thought off. Getting into a relationship with my bestfriend was the biggest mistake. I moved on shortly after took me time but yeah I did. I always wish for her betterment may she lives happily with whoever she wants. And may she finds someone who loves her more. I don't miss her anymore no feelings whatsoever have blocked her from everywhere. But today I saw her pic on one of our common friends insta. We used to hang out with same group and now I am not that good friends with those guys but she is. When I saw her pic after an entire year I felt so weak. I deliberately left this group so that she doesn't feel lonely. Never shared what she did to me to any of our common friends, kept it all within me. And now I have been side casted . All alone but definitely not lonely. I want to ask the people of this sub. Why do I feel so weak whenever I saw her?? I have absolutely no feelings for her nothing not an iota. In fact I regret loving her so much. Why do I feel so weak then? And by weak I legit feel like a loser .