I don't think neither one loved the other more. Max's world was Liz, and Liz would never love anyone as she loved Max. Liz said it best in ETOW
Don't you realize what you are to me...and you're always gonna be? You're the love of my life. Everyone else is gonna be second best. There'll never be another you.
and Max said it in Destiny
Liz, when I was in that room, and they did what they did to me. You're what kept me alive. The thought of you. The way your eyes look into mine. Your smile. The touch of your skin. Your lips. Knowing you has made me human. Whether I die tomorrow or fifty years from now, my destiny is the same: it's you. I want to be with you, Liz. I love you.
When Max thought they were really though he was devested, and he turned to Tess. When Liz found out that Max sleep with Tess, she turned to Sean. Max didn't love Tess, nor did Liz love Sean. They were substitutes for what they were missing. Something to feel the empty place inside of them, even if for a little while. I can understand Max's reason for turning to Tess just like I understand Liz's for Sean.
They both loved each other. They were young, and people make mistakes. They had alien destiny's, being chased by the special unit and evil alien enemies, and saving the world, all while continuing to go to school and act normal. It was hard and would take a toll on anyone.
Liz is not a saint, but neither is Max. They both fucked up at times. While one struggle to survive, one tried to forget. Did that make one more in love then the other? No, they both loved each other equally.
"If you make yourself happy, a little of that sunshine will spread onto others" - David Bowe