The funny thing is, at least according to Memory-Alpha, the novelization for TWOK has Preston listed as 14. A little too young for some Saavik-lovin, I think.
Saavik was helping him with his studies (mathematics, IIRC), and they'd become friends. I don't recall the novel suggesting they'd become more intimate than that.
The novel does
have David and Saavik as sexual partners during ST II, which really complicates matters for the events unfolding in ST III. We learned in "Amok Time" that a Vulcan hitting pon farr
for the first time must "mate or die".