In the Fantastic Beasts movie we find out that American magical community doesn't allow any relationship with muggles.
I think it's quite a sensible choice, considering that even the smartest and strongest muggle is completely powerless when it comes to mind-altering magic, which is available to an average wizard. It's not only dark magic either - Confundus, Obliviate (which it appears anyone can use) and other charms and spells come to mind, and I don't even want to start on potions.
Of course, wizards and witches are almost as vulnerable to these things as muggles, but they at least know about them.
We have a 'good' example of Merope Gaunt basically forcing herself on Tom Riddle Sr, and at least one example of a witch not telling her husband about magic until they are married (Seamus' mother) which seems like a very bad idea even if she had no malicious intent.
I'm sure there were a lot of other instances of magical people (not Death Eaters either) abusing muggles and messing with their minds.
The point is - muggles and magicals are in no way equal. So any marriage between a muggle and a wizard/witch should immediately fall under suspicions of foul play on the part of the latter.
So do we have any information about legalities involved in a magical person marrying a muggle in Britain? We don't have many conclusive examples. Was there any way for the muggle in question to protect themselves against manipulation and abuse?