What people wrote above is pretty accurate and exhaustive. The bottom line is that its a subjective issue depending on personal character, previous experiences, the way you were brought up and in what environment, religious factors and dozens if not hundreds of more factors. There's no binary way of deciding if something is wrong or right with these things, as long as you are not intentionally hurting another person you're ok. The way I personally see it is, I couldn't be with a very jealous person who goes all over me whenever I make a comment on another attractive woman and I do not expect my partner to be a saint and not look at other men and comment on them - that would be unhealthy for me relationship wise. It might work differently for other people though and that's ok too. The main part here for both sides is be kind to each other or at least don't be an ***hole to each other.