Commitment Phobia.
In 'Some Enchanted Evening', Compo was in hot pursuit of Nora who was reciprocating nicely, until he found out Wally wasn't returning and realized that Nora was actually pursuing him for real (gulp!). He quickly went into the run-Forrest-run mode and relapsed into his former phobic self.
Reggie Undsworth was what is called a "GU" (geographically undesirable), too far away to see often enough to develop a real relationship. These situations foster intense but infrequent encounters upon which Peter Pans thrive.
Compo looked up former girlfriends, a process called "recycling". As he learned with with Babs, this is dangerous territory in which to tread. People change, which can lead to hideous situations and rash emotional outbursts when old resentments kick up from within. Recycling is not for the feint of heart.
Compo was married the better part of a fortnight. No mention of his wife's name was ever made, which says something. He probably fell face first into this condition while well inebriated. Although he complained about the chuffing Pole who swept her off her feet and away from him, he probably was more relieved to be relieved of old what's her name, than resentful.
Compo was not the only one who exhibited commitment phobic behavior in Summerwine. In 'Of Passion and Pizza', Alvin told Entwistle that he was once engaged for 27 years. Entwistle enquired "why so long?", to which Alvin blithely replied, we couldn't decide on the curtains. This stall tactic is called a "lateral" (the antiquated term was side step), no actual movement in the relationship, but it has the implied feel about it of forward movement. It is like presentation of a friendship ring which is a lateral to delay or avoid presentation of an engagement ring.
I think we all have a bit of commitment phobia in ourselves, it is part of the human condition. Some have a lot more than others. Some have reason to have a lot more than others. It even spills over into the married population which explains the popularity of laybys (you can figure that one out for yourselves).
No, I do not think Compo was capable of marrying Nora. I think he felt safe pursuing her because he realized she was definitely not interested in a second marriage and felt safe in his own phobia.
Summerwine came out long before the commitment phobia phenomenon was really understood or publicized. This embodiment of the concepts in the Summerwine scripts reflects the deep understanding of human nature that the writer possessed and shared with us.
Aw, shut up Seymour and eat your choc ice.