Pay attention to her, sit down and watch her shows with her. Rub her feet, and try harder when you know you can.
Do the dishes for her, tell her she's beautiful, and make sure she knows you mean it. Play her games that she's into. Actually be interested in what matters to her.
Don't tell her she's wrong too much, even if she is... Especially if she is, that means she hears it enough elseware. Don't ignore her for other people.
Don't wait until its too late, when she has already packed her things and left. For the love of god do this today before its too late and you are sitting here like me with your life in boxes.
I invested everything in her, gave all I had. But I didn't do these little things, I fucked up. She didn't even say anything before she left, changed her number and blocked my social media. It can happen in an instant so don't wait until its too late.