Yes it's sad in a way and yes Barney and Thelma Lou eventually marry in the much later return to Mayberry movie . I actually wouldn't be surprised if that's one of the main reasons they did the movie. I don't remember if it was ever stated. I know Betty Lynn was heartbroken about Thelma Lou marrying someone else. I understand and shared that view for a long time. That said rewatching the show again more closely I don't think it's so bad she did . A late season five episode has Barney talking to a woman over the phone at the courthouse and Andy naturally assumed it's Thelma Lou but Barney reveals it was Juanita ! Either I didn't understand as a kid and later as an adult I didn't pay close attention but I thought Juanita by then was in the past. She was the side girl it seems all along. Yes Barney seemed to be commitment phobic but then in a way so was Andy so what was the difference? As I see it once Helen and Andy started dating Andy had no interest in anyone else. He didn't like Barney bringing around the fun girls and rejected Barney's attempts to find someone new for him when he initially thought Helen wasn't domesticated enough for Andy. Helen and Andy had an understanding they talked about being good with things for now and in time they would both know when the time was right. Say what you will about Andy or Helen some I think is fair some of it isn't but they talked things out if there was a misunderstanding they talked about that too . Barney may have genuinely cared for Thelma Lou and loved her but he also wasn't completely about her and they didn't seem to talk things out so yes what did he expect? She moved on . Barney never made intentions clear she was just supposed to wait? I guess. I do understand it's a big disappointment to fans I felt it too but now looking at how Barney took a lot for granted and was never completely loyal to Thelma Lou I think her moving on makes sense.
Edit: Rewatching this episode and Barney and Thelma Lou Phfftt I doubt Barney would have proposed while back for the reunion Yes he was disappointed but he left town and didn't keep in contact with her. She left Mayberry a month after he did. He didn't write he said. He always has an excuse he's busy with one thing or another. I think if Thelma Lou came in all adoring Barney would have basked in it for sure but it would be more promises and stringing her along he would promise to write and visit but would he ? I don't see him popping the question he just liked keeping things as they were. They even had an apparent classmate of theirs ( she seemed younger) . This classmate Netty thought so much of him and they danced together and he definitely felt better. Barney and Andy get back home and Andy suggest he visits Netty only a few hours away from where Barney is in Raleigh and Barney says maybe if he gets around to it he's so busy! So yea that's just Barney. I guess it took getting older for him to finally go for it.
It's not so much that he has to get married but you can't take nice people for granted.
Barney is definitely one of the all time great characters but not without some annoying flaws.
Edit: Rewatching this episode and Barney and Thelma Lou Phfftt I doubt Barney would have proposed while back for the reunion Yes he was disappointed but he left town and didn't keep in contact with her. She left Mayberry a month after he did. He didn't write he said. He always has an excuse he's busy with one thing or another. I think if Thelma Lou came in all adoring Barney would have basked in it for sure but it would be more promises and stringing her along he would promise to write and visit but would he ? I don't see him popping the question he just liked keeping things as they were. They even had an apparent classmate of theirs ( she seemed younger) . This classmate Netty thought so much of him and they danced together and he definitely felt better. Barney and Andy get back home and Andy suggest he visits Netty only a few hours away from where Barney is in Raleigh and Barney says maybe if he gets around to it he's so busy! So yea that's just Barney. I guess it took getting older for him to finally go for it.
It's not so much that he has to get married but you can't take nice people for granted.
Barney is definitely one of the all time great characters but not without some annoying flaws.