A couple has a much better chance of surviving Europe. The old motto “Strength in numbers” applies heavily to couples who are traveling. Not only will two people have a better chance of finding where they are going, helping each other through sickness, finding help during kidnappings, keeping an eye out for pickpockets, finding the U.S. embassy when everything goes wrong…but they also have an easier time of taking pictures wherever they go. Selfies can get old quickly. It’s nice to have a wide shot now and then.
If you’re traveling as a couple or threesome or more, be ready for the problems. If you are by yourself, you do what you want. If you’re with one or more people, every decision must be a group decision. This slows down traveling greatly. Your best bet is to designate a travel “dictator” or “president” who can call all the shots. Of course if that person does a bad job, the other people in the group can mutiny and select a new leader. If there are just the two of you, this can ruin your trip. Hopefully your leader will be the person who is the pickiest and the other person can just go along with whatever she/he says.