Few weeks ago, my SO and I were on the sofa watching videos on his phone. We gave up after a while and I went back to watching TV. He moved his arm to rest of on top of my head, which was uncomfortable so I asked him to move it back. Then we titled this phone away from me, so I looked enough to see it (I know I shouldn't have, I know). He was on a girl's Instagram scrolling through her photos, which tbh i was like oh well that's fine. But then he specifically opened a photo of her with her butt out and zoomed in? All while he thought i couldn't see? I am panicking a bit over it. 

If he showed me her and hone "isn't she pretty?" (I'm pansexual) I'd probably agree but the fact he was hiding it really upset me.

This might not make any sense, I apologise. Am I justified in being upset/worried?