I think it's about a guy who goes to see his ex-girlfriend get married -- "her holy vows"
"Dirty thought occurred to me, could have had 'em if I wanted" (he could have married her if we wanted to)
"How Could I know" (I'm guessing this is an exclamation of his regret -- how could I know that she was going to end up with someone else or how could I know that I wasn't going to be able to stop thinking about her. He regrets letting her go.)
I think it's about a guy who goes to see his ex-girlfriend get married -- "her holy vows"
"Dirty thought occurred to me, could have had 'em if I wanted" (he could have married her if we wanted to)
"How Could I know" (I'm guessing this is an exclamation of his regret -- how could I know that she was going to end up with someone else or how could I know that I wasn't going to be able to stop thinking about her. He regrets letting her go.)