Oookay, I think my previous critique of this question was valid and I don’t think I was too harsh about it, but apparently the moderators disagree with me. Let’s try again:
I find your question offensive because it’s such a sweeping generalization. At the very least, I wish you’d written “some” before “women” in your question title.
Your observation doesn’t reflect my experiences at all. Of course, I’ve encountered women who seem to define themselves by their relationship, but I’ve also encountered women who don’t, and men who do.
I think your question would be a lot more meaningful if it was about people. “Why do some people define themselves by their relationships, whereas other people stay more consistently ‘them’ no matter who they’re with or not with?” That is an interesting question. Personality types, etc.
If you think there’s a bigger trend for women to be this way than men, that’s fine but I think you should talk about it in terms of a trend. This way, you can avoid making derogatory generalizations about massive groups of people.
Although, like I said, this doesn’t reflect my experience, I think if there IS a trend for women to define themselves by their relationships, it’s because of the patriarchy and sexist socialization. I move in pretty ‘liberal’ circles, so I can imagine my experience of the world is limited in that regard (as everyone’s experience is limited, which is why I think we should avoid making generalizations – stereotypes, prejudices, assumptions – based on our experience).