See my comments on the distinction between need vs desire in this thread.

> should be something that is a bit more in-depth than "you don't need to have sexual intimacy in your life to be happy

That's correct. You can feel happy doing a variety of things, such as hobbies, work, dining out with friends, etc. Your not engaging in sexual intercourse does automagically stop happiness in tracks.

> ... and feel fulfilled."

Nothing in the dictionary definition of the word "fulfilled" -- "satisfied or happy because of fully developing one's abilities or character." -- indicates necessarily having sexual intercourse.