This is becoming normal during the day. I have a cat, Tabby, she is a loner, just needs I, me and myself. Then we have Roschti, a cat belonging to the neighbour. They sort of grew up together, but in their own territories on different sides of the fence. However, now being older cats, 18 years old, they develop new ideas.
Tabby, a lady, is quite happy to stay where she is, but Roschti, the man, has discovered that life can be more interesting on the other side especially when Tabby always has food ready behind the window. Roschti waits for the opportunity and when no-one is looking he hops through the window and helps himself. This does not bother Tabby so much. They seem to have come to an agreement. They even sleep in the same places, although holding a safe sociable distance. This has become the new normal.