Paul Newman and Joanne Woodward had the glue. By "glue," I mean they they had similiar facial features. Paul and Joanne also had similar style and compatibility that enabled them to stand the test of time.
I learned a long time ago that a relationship without chemistry is a time-bomb waiting to happen. You may be attached to someone, or even love them, but if you don't have chemistry you will most likely meet someone with whom you do have chemistry. That is the person you will feel you need to be with to feel alive and connected to the world. At times you might feel as if you cannot breathe without this person and if you don't see that individual an emptiness ensues.
You also become excited with the thought of seeing them or just thinking about them. This intensity will , of course, wear-off over time, but in a healthy relationship it is replaced with security and love. And even though the intensity fades, there are remnants of that intensity established in that powerful first stage and will emerge throughout the life of the relationship.
It's sometimes hard to tell with heterosexual couples the similarities present in their faces. The hairline, which often recedes in men will make it difficult to see. A friend of mind went through an amicable separation and her soon-to-be ex-husband is now dating a woman that looks like her, but has blond hair. I saw it so clearly, and because she knows me and my theory, she identified it right away. Her husband is not consciously looking for someone thats looks like his ex, but he is subconsciously looking for someone who attracts him. And he may have almost got it right with my friend, his first wife, but not exactly right. The facial features are so subtle that getting it right is a science!