Sexual selection doesn't end at being attractive. It could be everything from killing competing suitors to making sure kids have a good career. Just as every organ is a reproductive organ, drawing the borders of sexual selection is hard. Everything cashes out in reproduction, where I try to draw the line is that the survival of individual animals against the forces outside the population is not, so getting food and getting away from predators is not. But pretty much everything inside the population is. But even getting a lot of food can be an aspect of it... crap. The point is that the traditional/popular views of evolution tend to be "survivalist" and basically this intra-population competition / sexual selection stuff is largely everything else that it is not directly survivalist but is about competition for things beyond the survival of the individual. Be that sexual partners or childrearing.

And yes, in this sense Mr. Dumb taking a knife to the heart in a pub and his girlfriend hooking up with someone else is an example of this intra-species competition...