Yikes. Some of these responses... look, the chance that it's purely love or lust is very slim. There are a million reasons why people sleep together. Humans are complicated which makes sex complicated, but sadly, it's just a bargaining tool for a lot of people. If two folks are intimate, then one person always wants it more than the other, but the one who's less receptive to it tolerates it for certain reasons. It can be out of a sense of obligation, it can be to get ahead, it can be due to peer pressure, it can be to stop our partners from straying. People are petty and we're very susceptible to emotions that make us seem weak. We want solidarity, we want to believe we're improving our relationship with the person we're with. These are the types of feelings that cause us to have sex, but this doesn't really constitute love - it's us marking our territory and trying to protect our egos. Nor is it lust, otherwise jerking it at home would suffice. Instead, we want the physical aspect in order to feel validated and attractive, which again is a symptom of our egos acting up. Either way, it's complex.