my friends ex boyfriend started out normal then got increasingly hardcore religious. he didn't seem to realise that hell isn't a threat if you don't believe in it. luckily she told him to fuck off. i think he was arrested for possession of child porn later on. but he was a scumbag and not representative of religious people in general.
doesn't really help answer the question does it?
I think its a good answer, you gave an example of how at first it may have been working fine but as one became self-ish in the relationship that is when it ended. So that tells us that when someone tries to force in these kind of relationships it could end bad.