I spent some time in only secondary relationships. It gave me the benefits of being both single and in a relationship! I got to learn some solid life skills and self sufficiency, while still having companionship, connections, and sex.
But I had to be pretty committed to the idea of spending some time as single, first. Once I liked that pretty well, then I was able to adjust, and okay, explore some secondary relationships, without feeling too lonesome or unimportant. My primary was myself.
But if you don't like the idea of being single, then I don't recommend it. It did get a little lonesome sometimes, especially around the holidays.