I think your friend saying that it is a totally biological thing is totally wrong, but I do think we are made to have sex. With that in mind, one needs to consider other's feelings. I have had premarital sex and it was always consensual and from my point of view, my partner and myself did not have emotional problems when we broke up.
I am now married and wouldn't dream of hurting my wife by having sex with someone else, but I actually think I am a better lover because of the multiple partners I have had. My wife would agree and says she is better because of multiple partners. That being said, it is not for everyone.
I say as long as no one is hurting anyone, than to each their own. Though I do think alot of people, both male & female, do not think enough about what they are doing and do end up hurting themselves, their partner or someone else.
