When you get to the 'comfortable silence' point in your relationship where just the company of your partner is enough.
Knowing that there is always somebody to do something with. Whether it's a walk in the park or a trip to the cinema. They have your back and don't let life get in the way of spending time with you.
Those little inside jokes or mannerisms you share that nobody else would understand, but you both appreciate.
Listening to a song you have enjoyed for years and finally relating to the meaning because it reminds you of your relationship.
Those looks. You know the ones we mean, the ones he gives you that scream "God, I love you" or "You are so amazing." He might give them to you when he thinks you aren't looking, but you see them.
The tiny details in someone that you start to love. His smile. The facial expression he gives you when somebody is annoying him. The look of concentration he has on his face when watching TV. His delight when you surprise him with breakfast in bed...
After an argument, having that shared "let's not fight" moment that makes you feel all warm and fuzzy that you don't always get with friends. Let's face it, with friends it's more like "hey bro, we cool?" Or you both just behave as if nothing happened in the first place which isn't quite as satisfying.
Being vulnerable to somebody isn't always a bad thing. Having that one person you can open up to about anything, even if you choose not to is comforting.
Finally getting to take part in those things you could never do with friends. Like that British Bake Off inspired couples cooking class you can now enjoy. It might not be everyone's cup of tea, but it's a thumbs up from you and your partner.
Getting told by your partner that they love you or getting a random kiss when you least expect it. We're blushing right now, but don't tell anyone.
Travelling together. Even if it is just to your nearest pub that you haven't tried yet, being able to experience new things with someone you love is wonderful.