Interesting!! I think we need to distinguish between the different levels of the topic. At the bottom, and from an evolutionary point of view, the ultimate goal is to preserve species through procreation. However, evolution via natural selection has built rewards at higher levels in animals, including us, to do this.

Different than other animals, except possibly for bonobos (our closest relative in the evolutionary tree beside chimps), we humans have sex not just for procreation. We have sex anytime we want. Other animals do it only at specific times of the year, or at specific times of the month as in chimps, because it is solely for procreation.

So, sex is more than just for procreation in humans (and bonobos to a lesser extent), it is for social bonding as you mentioned, which is also necessary for the survival of species. For example, it was observed that in bonobos, sex is used as a way to diffuse a conflict. We use something like this "make up sex". Also, females have emotional attachment because their brains are designed to care for their offspring.

Now because we have large brains, and we are self-conscious, these emotions and capacities have been extended way beyond their original purposes. Something like math, our brains weren't designed to understand math and quantum physics, but out large brains are capable of doing them.

But this doesn't degrade the meaning and existence of love. It is a fact that we humans love each others, regardless of the underlying processes and purposes. It is beautiful, and many great artistic works have been done in its name. Actually one can argue that love is the most powerful tool humans have.

A question to contemplate on: can you imaging a romantic relationship without sex?