Yes, lack of girl talk does seem perplexing here... And yes, I do believe in the 1950's and 1960's, boys talked alot about girls, if they weren't losing their virginity at age 15 as they do now, they still (well some of 'em) had alot of hormone activity for the opposite esex.
Ennis doesn't know Jack's "situation." The queer thing would be so out there, especially given gay sterotypes of the early 1960's, I'm sure it wouldn't have crossed Ennis's mind that Jack might be gay.
Of course, Ennis doesn't seem the prying type. If Jack want's to volunteer info, Ennis will listen, but that's about it. They do discuss their plans to get each get their own place, but maybe that's to let off steam about having to work for their S.O.B. boss.
I wouldn't expect Jack to ask Ennis to many"general girl questions," even if Jack was straight. It's just one of those things, after you find out a guy is engaged, you usually ask questions about "Alma" in this case. I noticed Jack wasn't too inquisitive about Alma.
I would, as a polite courtesy, "oh, she sounds nice, gotta a photo of her." Of course, Jack might be in denial that he's falling for a guy whose getting married. Don't want to hear that. Means their relationship can only go so far.