It is more expensive for sure. Two depreciating vehicles wearing out components and burning gas and requiring license, insurance, etc. Can you afford it? If so, then no worries... except for there being some added hassles with two.
Nice to have backup in case of breakdown, but also twice as likely to experience a break down!
Also nice to have smaller, more nimble, easier to park, more offroad capable vehicles.
Lots of upside to partners having their own space, and sharing space when they wish.
I've lived with 3 different women in a '84 Toyota pickup with two different very spartan homemade campers that were not very big. For them it was a "novelty". They lasted for 6-12 months... though I later ended up getting domesticated and living with one for 20 years! I don't think more space or separate spaces would have helped much. Rather they wanted things that nomadic living made difficult. Different strokes for different folks...