Some believe the biological point of sex is reproduction. Some think the spiritual point is explorative and based on experience, love, blah blah blah ;)
And then there is what you are explaining which I think is from the angle of conquest no? Or did you just simply mean the fulfillment of instinctual directives? You satiate desire? I can think of pointless situations for each all of these examples and views. I think its easy to reduce sex into something that just simply is, and needs to be done whenever possible. I understand that point of view but I don't agree with it.
Just semanticly I can create a few situations where I don't see any situation where pointless sex doesn't exist.
Here's a quick one: you've had sex 4 times and are raw... Numb, and couldn't achieve orgasm again if you wanted. Disregarding the woman in this situation (as OP already was anyway) sex again would be pointless. In the context of love, marriage, or commitment alone there are endless examples of pointless sex. Sex without reproduction from a biological standpoint can argued to be pointless. There are probably some grey areas in there too for dominence, pleasure, instinctual commands... But I think as you stated, the point of anything is that things point. So how do you argue against such a broad generalization... I don't think the point of sex is to simply "have sex" its any number of irreducible things that make up sex... To achieve orgasm, to dominate/be dominated, to grow spiritually, to have children, to explore, etc. Etc.
The point of breathing is to breath. In a way that's correct... But in reality its to sustain the process of life through respiration, to calm down, to smell things or to be tested for alcohol content.
I just agree with the earlier guy who posted suggesting this guy not do this because it most likely won't make him feel all that much better about the earlier exchange and it invites the possibility for problems by bringing this woman (however temporarily) into his life.
Not to mention he's giving her a chance(however small) to ensnare him.