I'm not sure exactly what you mean by social bonding, but it's pretty common knowledge that bonobos, which are our closest relatives, use sex as a form of social bonding. They use it after fighting, they use it to socialise, and they pretty much have no taboos about sex.
Dolphins also use sex in non-reproductive ways (such has having forms of sex that can't possibly lead to reproduction) but I'm not sure how much they bond over it.
Bonobos also use non-reproductive sex in social bonding. In fact, humans is the only species that uses possibly reproductive sex in bonding. It's therefore perfectly possible this is a quite recent trait in human evolution that don't need to be a universal that applies to everybody.
This being said, I fail to see how what other animals do is relevant to us. Humans are humans, and I don't think basing what we should do on what other animals do, rather than what we're personally naturally drawn to as a species, is conducive to a better self-understanding.
It is relevant for us because we are a hybrid species (at least Eurasians have Neanderthal ancestry). Since the research on exactly what traits Neanderthal contributed to our genome is still in it's infancy, we have no definite answers on this yet. My hypothesis is that it is neurodiversity that is the Neanderthal contribution to our genome, and that this can explain asexuality and why our species is both monogamous and polyamory. This combination would not really be possible in a non-hybrid species.
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