There are life-long partner bonds/agreements in nature (albatros for instance). Therefore the claim that they do not exist is probably just ignorance, and if I may speculate, this particular councellor has had a bad relationship or is unable to commit himself to one and assumes everybody is the same as he is. A common mistake to make. To claim that marriage is unnatural because it is cultural is also a dubious claim, since for instance the albatros goes through a bonding ceremony before the marriage. That is also a form of culture. Culture is not unnatural. Many species exhibit culture, not just humans.
