It's often hard for the opposite sex to read each other. Women seem too complex for men to comprehend, and men seem simple, unthinking, and unpredictable to women. If you know what you're looking for, however, there are always signs you can read in a person's behaviour. Add that to the fact that we live in an age or insecurity and anxiety, it can be hard to tell if when he says "I love you" he means it, or if he feels it even though he hasn't said it yet.
He Makes Sacrifices
When your partner is in love with you and committed to the relationship, he will do anything in his power to be with you. The sacrifices he makes can take form in many ways, he could move to be close to you or something as small as spending a romantic night with you instead of a night at the sports game.