I am going to offer a slightly different take on this, from personal experience…despite the fact that the OP essentially has his answer.
To me it’s more than just faith differences, how to pray together, etc., it’s also a case of how faith diferences color one’s world view. Catholicism has produced people like Augustine & Thomas Aquinas. Catholicism is a faith which has the context of a theology based upon a detailed philosophy; for example, Aquinas built upon Aristotlelian concepts to some extent. However, protestantism simply doesn’t have that background, perhaps because it may not need it, and that lack colors the views of its adherents.
On a tangible level, I know someone who was/is Catholic…he dated a Baptist whe he and she were both in their early 20s many years ago. She was a lovely young lady, very faith-filled - but the relationship eventually went nowhere because of the different mindsets of the faiths. The guy was getting a BA in philosphy. He liked having detailed, thought-provoking discussions…but his girlfriend’s “philosphical inquiries” generally were limited to, “what does the Bible say?” She was not stupid, far from it…she just had very little real intellectual curiosity, based upon her faith’s apparent lack of need for such curiosity. So eventually the relationship failed, basically because – I believe – one faith was simply a great deal “intellectually deeper” than the other.
Although I understand that certain protestant faiths - i.e. Anglican - may be closer to Catholicism that others, marriages often have a great deal stacked against them today, let alone if both parties have divergent world views from the get-go. Catholicism has a very rich intellectual tradition, which is sometimes - note sometims – lacking in protestant sects, and that difference may infuse (infect?) a relationship.