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The original Lois & Clark aired in the 1990s. These are the X-Files years where Chris Carter simply ignored the issue of sex regarding his main characters for six plus seasons. And it worked!
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The topic is still omnipresent but not as frantically discussed. Some people will claim that this is because teens having sex/people having sex before marriage has become too much of a norm. The truth is, the number of teens engaging in sex has decreased in the last ten years. In fact, Castle took for granted that Alexis would wait until college. And while that was far less likely with Mandy from Last Man Standing, there was no corresponding pressure placed on Eve to "grow up right now." (Not that any guy without massive self-confidence would mess with Eve anyway--see above image.)
Sex is no longer being used as a coming-of-age ritual, not to the same degree as it was thirty plus years ago.
Still, in television world, if two adults with no religious upbringing don't sleep together before getting married or moving in together, the question of "Why?" arises. What's the background?
My background for Lorry and Clark is as follows:
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Lorry has great insecurity about relationships, which was compounded in college by the Linda King episode (see "The Rival" from Season 1). Lorry was dating a confused guy whom Linda stole away. This event is one reason Lorry is so definite about never dating a guy who isn't totally and completely 100% out. He is wary with Clark, whom he doesn't entirely trust until the end of Season 3. And he is tired of having his heart stomped all over. He has more sexual experience in some ways than Clark but that experience is fairly limited.
In many ways, Clark has a much broader view and understanding of sexuality than Lorry. Although he didn't come out to his parents until moving to Metropolis, he traveled a great deal after college and consequently had experiences that actually make Lorry look a tad naive--which is something of a staggering revelation to Lorry who has to readjust his image of Clark as the naive country boy (Clark is--and isn't).
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So Clark and Lorry are cautious, which doesn't preclude other approaches. But cautious. Which keeps the timeline intact and makes it possible to put off the episode "Soul Mates" until the fourth season.