I don’t want my ex back, but him moving on bothers me.

it has been almost 6 months since me and my ex boyfriend of three years broke up. He told me that he had been losing feelings for me for the last few months, and I agreed that we were incompatible despite still having feelings. we've been no contact since the breakup and I had him blocked on instagram. Today, he hard launched his new girlfriend on his Instagram story, and one of his friends sent me the post. His new girlfriend is a friend of his whom I had suspected he had a crush on but didn’t want to cause drama so i never brought it up. He had blocked all of my friends from viewing his story, so he clearly didn't want me to find out and didn't think that one of his own friends would send it to me. I later found out that they started seeing each other a month after we ended things. I feel like I should be over it already since it’s been months since the breakup, but having him flaunt someone new hurts. It’s also a bit of an ego bruise for him to want to hide it from me too while doing it in such a public way. I don’t want him back but it bothers me that he moved on with someone he was friends with while we were dating. He definitely did not cheat, but moved on more quickly than me and my self-esteem is taking a hit. Has anyone experienced something like this?