Egoism is not predicated on isolation or hermeticism. That's more Schopenhauer than anything. Egoism is the rejection of any sort of higher essence, fixed idea, alien ideas or higher cause. Rather than isolating the self, the egoist brings things down to their brutal, feral, and immanent thoughts, desires, and power. The egoist, as such, rejects all sorts of morality as well as God, Man, the State, Society, and other such things. You see, each of those exist separate from the self and only operate through fixed patterns. There are only some things which are acceptable under those, and, as such, the egoist must sacrifice their own interest in order to accept that in favor of the interests of those ideas.

But, again, this isn't the rejection of all relating with others. Rather, this is the rejection of all sorts of mediated and fixed relations with others. In the place of this relations are laid bare as unions of egoists. A union of egoists is a truce between egoists so that they can work together for mutual benefit. It lasts as long as it is beneficial to all involved and operates fluidly. Indeed, while we exist within a society, they do exist here and now. You can find them in children at play, in friends going to a bar, and in lovers together. Children who aren't having fun will stop having fun, friends won't go to the bar with their friends if it's not something they desire, lovers stay together as long as they feel love for each other, and, with each of those, they change and decide on things fluidly through discourse with each other. This is what's referred to as intercourse, that is the brute, immanent relations between people operating on the basis of who the other is rather than on the basis of mediations of relations.

While this doesn't entail hermeticism, this does entail the rejection of the state, of sacred property (aka property built upon respect and morality rather than the brute facts of power), of Man, of mass organizations, and many other forms of relating to each other. All of those things are based upon sacred things, which are necessarily alien to the self.