Early 70s Sci-Fi book, I believe it was 2 humans (man and woman) on an alien planet... (I don't think they were stranded, I think they were there to explore.) There may have been a few more people with them. But I mostly recall just the two.
I believe the man was doing something and to keep the woman from distracting him or disturbing him while he was doing it, Taught her about Conway's solitaire game "life"
This "game" had just been described in Scientific American magazine (October 1970 issue) So the story must have come out withing a year or two of that.
I recall the each chapters had an image of different small "Life" patterns, with more complex pattern as the chapters progressed.
So while she is "learning" and "exploring" the aspects of the "Life" game, we the readers are getting a thorough intro to the game also. Pretty sure there were many images similar to the ones above showing the patterns and permutations as she learns how the "game" can progress. Mostly simple ones that either die or become stable in a few generations.
I think the man discovers they are being spied on, (either by aliens, or the other humans on the exploration team with them) who want to obstruct their mission.
So the man takes the woman to a pool of water, (Swimming pool? Pond? creak? Lake?) and they start having sex. WHILE doing so, they start communicating through Morse code, by him "throbbing" his "member" to inside her, and her replying by "clenching" back on his "member" while its inside her.
Its possible I might be me confusing 2 stories in the same series (i.e. the "Life" game was in 1st book and the Morse Code was in the second book in series.) But I am sure they are linked. (Same book or same series)