Am I crazy?

My boyfriend and I have been dating for 6 months. Things are slowly getting more serious, and I feel like things are finally looking up. But his ex girlfriend of 4 years, whom he had bought an engagement ring for, is liking his Instagram posts.... At first, I was livid (she cheated on him a lot, and pretended to be my friend before they met), but now I'm feeling extremely insecure. She was his first love.  I know he will always have feelings for her, but I'm struggling with the fact that he still has pictures with her on his social media, as well as her being the kind of girl that is ok with being a homewrecker and cheater. Advice is welcome.