In 1963 Good Girls still DIDN'T!! And out West, in the sticks, even less----I am betting that Alma and Ennis together may have had a few kisses good night---and held hands alittle. that would have been about it. I doubt they were ever actually together alone for any length of time.
first---Ennis didn't have a car, and no way to get one---so there go many dates, that someone didn't bring one or both of them to social gatherings so they could get together. He and Alma met in school probably, before he had to quit, and before he and his brother had to move cause sister got married and moved--and they couldn't make the rent in town anymore.
second-With Ennis being raised on a working ranch with his brother---they don't get much time off--for much of anything---a few church socials and a few community dances would be about it--Ennis wouldn't have had the time or the money to get anywhere to "sin" so to speak.
He may know what goes on, after all his sister got engaged and married, and his brother just got engaged---and he himself considered himself engaged, but actually being together physically for him and Alma--would have been mostly difficult at best.