When my best friend and I were in high school, we decided we were going to write a book together. One week later, we weren't speaking to each other. We couldn't agree on what the characters would be named, what they would look like, what they were going to do, or what they were saying to each other. We won't even get into the delusion that we could actually write. Needless to say, I have a great respect for the special skills of authors who can collaborate to tell a single story. I mean ones who really collaborate, not become a brand with a second author. I am baffled by how they can make it work as a truly equal effort, but some very successful teams of friends , husbands and wives , even mothers and sons  have proven it can be done.
In the Romance genre, there are several well-known writing teams available from the Library. Have you tried any of these?
Lydia Dare  (aka Tammy Falkner and Jodie Pearson)
Judith Michael  (Judith Barnard and Michael Fain)