Lily Evans was his everything
To say that he loved her would be an understatement. Love is not a big enough word to describe how James Potter felt towards Lily Evans, and I doubt I'll find I word that is. She could break his heart with a single word and mend it with another. She had cast her spell and he had fallen helplessly under it.
He was falling deeper and deeper and it was going to end in heartbreak.
Severus Snape loved Lily Evans. But he was too much of a betraying, over obsessed creep to win her back.
Sirius Black loved Remus Lupin. But Remus was too caught up in his own problems to notice Sirius.
Emmeline Vance loved James Potter. But she was never even competition with Lily and went all the wrong ways about dealing with her problems.
Then everything was shaken and it was near impossible to tell who the right person to love was.