<human>: They split up two years ago but have remained friends since. She mentions him occasionally and still has some mementos from the relationship which I don't mind at all. But this post makes me uncomfortable.

The picture is just of his face. The caption reads something like: "Found this on my old phone. It's from a picnic we went on a year ago and it's too nice not to share especially since I've been missing your face lately." 

She has older pictures that she posted two years ago while they were still together which is absolutely fine, and I don't expect her to remove them. They don't matter to me. But the fact that she posted this now while we're together and that she said she missed him is making me feel pretty bad.

I obviously am going to talk to her about it, but before I do I want to make sure I'm not overreacting or reading too much into her doing this. Am I right to feel uncomfortable about it? And how do I go about telling her I don't like that she did this?

Can you provide a brief overview of the text?
<bot>: Five months into our relationship, my girlfriend posted a picture of her ex on instagram with a caption saying she misses him. I'm pretty uncomfortable about it.