It doesn't seem like this strategy will continue to be effective when you are no longer a young man. Is this a short-term strategy?

Why does it seem unlikely to remain effective? He radically improved his general social skills, and made himself much better at initiating new relationships (of all kinds, not just romantic). Why would said skills atrophy?

It doesn't seem like this approach will yield stable and reliable companionship into old age.

Why not? At a minimum, why would being better at starting new relationships make him worse at maintaining ones already in place?

There is no mention of the desire for offspring in this post. Historically the point of sexual relationships has been offspring, the nominal "reason" for dating has been to find a suitable partner with which to raise offspring.

History need not dictate our preferences. If we demanded that all sexual relationships lead to children homosexual relationships would be illegal, as would ones where one partner was infertile, and marriages would be dissolved upon a female partner reaching menopause.

Sorry if this post is unbearably quaint, but I can't figure out why you're even bothering with all this. I mean, save yourself the trouble, just remain celibate or use prostitutes.

Because he wants to be in the best relationship he can be, with the partner(s) he is most happy with. Learning all this stuff makes it more likely that he'll achieve this goal. Presumably this makes (at least) two people happier, Luke and his girlfriend.