This, applies solely to a partner. A healthy relationship must also include a good se* life. If your soulmate is your partner, it is of utmost importance that the sex is good. You really don’t want to spend the rest of your life being bored and unsatisfied, do you?
5. You have started completing each other’s sentences.
This is less romantic, and more about how the two of you practically share a brain. The two of you know so much about each other, that in many cases you can communicate just through ridiculous hand gestures, and through your eyes. Completing each other’s sentence stopped being weird, and started being regular, long time ago.