Who wouldn’t bend on the religion issue?
As a Roman Catholic I spent the first twenty plus years of my life thinking that Catholics only married Catholics. Thankfully, the right girl came along, and even though she wasn’t Catholic it opened up my eyes to the power of God and that he will put the right person in your path.
Did it cause issues early on, sure it did, but someone has to be willing to bend to make certain things in life work. If you close your options to only people who share the exact same faith you do, you are narrowing it down to a far smaller number of possible long-term mates.
My guess is that whatever the issue was, it was major and neither was willing to see it the other way. Compromise is big in any relationship. If the love isn’t strong enough however, then compromise is harder to come by and live with. Apparently, it wasn’t in this case.
I was willing to marry a non-Catholic at the compromise our children would be raised Catholic. My girlfriend / wife was okay with that, my Lord is okay with that, but if she wasn’t, it wouldn’t have worked. Everyone is different though. I get it.