Am I being used for sex?

I have a friend, that I met awhile back, and since then we established that we’d be friends with benefits. Two weeks ago, I had a pregnancy scare, and thought it would’ve been ok to share this with my sister (isn’t that what siblings are for?)

Since then, anytime we get into fights she always brings up that, “I lack self-esteem” because I’m having “sex with someone who doesn’t care about me” Sex isn’t everything with this person, we do go out, and have in-depth conversations. When I voiced that my personal life isn’t her business she claims it is, “as your sister”

In my honest opinion, I think there’s no such thing as being used for sex, if two consenting adults are willing to be intimate with each other then no one is getting hurt-unless its rape. Not sure if everyone will agree with this analogy, but it’s just how I see it. So am I just a pair of holes lacking a conscious, and self-love?