To know that you love the right one, it is instinctual. Things that normally bother you still do, but when they do it, it's somehow more okay. You'll know because the very thought of them diminishes the demons creeping below your skin. They make breathing easier and waking up in the morning a blessing, not just a task. It is looking at a person and knowing deep down you would do anything for them, even if it meant hurting yourself. It is being able to do absolutely nothing but sitting with them yet having the time of your life. It's the agony you feel at the concept of them leaving or anything happening. It is spending time with them for 12 hours and feeling like you just said hello. Knowing is something that happens so deep in your heart that no logic or reasoning helps. You just know, not with your brain, but your heart.