However, one big concern is security. If both partners got access to the same wallet and one of them falls for scam, all their Bitcoin could be gone forever.
Another issue is inheritance planning. If Bitcoin is held private by one partner and they pass away sudden without sharing access, the other one might struggle to get back the funds. And what if the couple ends up divorcing? That could turn into a whole different mess.
Yes, the couple might invest in Bitcoin together because they are together and trust each other. There's nothing wrong with that if the couples investing together, but what you indicated earlier will be a major issue: which is divorced. Because if they are no longer together and one person holds the private key, there will be a big war, especially if the husband holds the private key; he will not want to release the private key so that they can share what they've invested so far with his wife, and if the husband refuses, and if he does not, they may cause a great deal of trouble by starting arguments between the bride's and groom's families.