Before concluding the question in the title, do you feel being vulnerable is a weakness or strength? Because your answer and perception are quite important for you, to open up in the aspect of sex. Mostly, the word vulnerability is considered as a weakness or a bad term that is used for low self-esteem and emotional strength, but indeed this is a term that must be used positively, especially when it comes to intimacy in a relationship. If having sex is the ultimate form of showing love, then being vulnerable is the ultimate form of showing yourself the way you are in a romantic relationship.
Forget about the economic and social vulnerabilities in a person, for a top-notch intimacy in a romantic relationship; a person must confront one's physical and emotional vulnerabilities. We may have sex with various people with various emotions and feelings. We sleep with hookers for having sensual fun and fulfilling sexual fantasies, we sleep with random people we meet on virtual and real spaces to get rid of stress or to explore one's self or orientation, but we sleep with our loved ones to express our intense emotions in every possible way. Of course, you can be that person who sleeps with any kind of person to express the love and lust, there's no wrong in it. Do you know, the vulnerability in a person differentiates the sensual experience of one's various sexual encounters?