Kinda ticked at my friend but I could be overracting?

Well for about 2 months, my ex and I been talking again as friends. The thing is I can admit I still care about her a lot, my friend I've known forever we tend to talk about stuff going on in our lives. When I told him I was talking with her again, he felt it was a bad thing for me doing it. Because we had a long distance, I plan on going to see her soon just as friends. But he feels that would be bad again, but the thing is I really do want to go see her. Well then a few days ago I was my instagram and I noticed on one of her pics he liked it. Wasn't some funny meme but a selfie, for some reason I feel insulted of it. I know it seems silly, but he always thought I should stop talking to her. But he continues do to so. Again I feel like an *** for feeling like this.