From the Bank's point of view, an approved transaction is an approved transaction, meaning that if you indirectly approve the transaction (as the cardholder) by giving the card to your spouse/child/friend/parent/significant other, thats all they are worried about. That being said, modern fraud detection algorithms are particularly sensitive - especially since they are tuned towards the false-positive side on purpose (better to catch a few non-fraud transactions then to let some real fraud slip by). If you shop at significantly different places than your significant other it may trigger a fraud alert on his card so that is something to watch out for, (same with a child using his parents CC to buy online game accounts - happened to me when I was younger).
On the side of the Merchant it is their responsibility and their financial liability (in some cases) if they let you use someone elses card to make an unauthorized purchase so you may well be denied the ability to make the transaction. In the worst case they are not allowed to confiscate your card, and if they try to do so (while it is messy) calling the police and having your partner verify by phone/in person that the card wasn't stolen may be required. Usually if you share the same last name merchants will let you use the card. If it is a debit card they shouldn't care as long as you have the PIN.
If you are really worried you can have your partner sign the back of the card with the note along the lines of "signature - I authorize Victoria to use this card". This will - at the very least - keep them from being suspicious enough from confiscating the card. I have a coworker that signs his with "check ID please" so he gets carded every time.