When I was a kid back in the 50s, I belonged to a Boy Scout troop sponsored by a Presbyterian Church. Once a year they had 'Scout Sunday' and invited all the troop members to attend. I asked my parish priest if it was ok if I went. He said to the effect that I'd better go because that church did a lot for the kids and I owed them that respect, and BTW, say hello to Rev. Anderson while I was there. They were good friends.
I think that not attending another service was a myth that a lot of people believed, and not actually a church rule.
“I think that not attending another service was a myth that a lot of people believed, and not actually a church rule.”
My Methodist Mom and Catholic Dad were not allowed to get married in his church back in 1945; they had to have the wedding in the rectory. When my Mom’s cousin got married at her church in 1957, we were allowed to attend the wedding service, but were told it would be a sin to participate; even singing the hymns would have been wrong.