It's not wrong at all!!!!! I freak out when my SO does that... He's learned not to or he'll have to hear about it for hours lol. He shouldn't be liking another girls photo, it makes me look stupid when other people see my boyfriend did that, and it shows the girl that he likes what he sees. NO THANKS!
Because I am confident in my relationship and self. If he is going cheat or leave or lie or whatever he is going to and it will have nothing to do with that picture. I know exactly where is stand with him so I don't care I know that it doesn't matter what she looks like she will never compare to me in his eyes.
I say no because it doesn't matter what my husband likes on the internet, neither of us do it's just a picture. Just like porn or magazines he comes to my bed at the end of night. Plus a healthy relationship has trust and respect. I assume he doesn't parade pictures of women in front of you, i think that would cross the line just like flirting with others in front of you is not okay.
Depends if you trust him and he has given you reason not to. If he's liking nudes or girls he's been with before that's just not okay. But if it's a friend's picture and he's never cheated then it's fine.