A man is obviously in love if he makes things all about his girlfriend. Compliments, gifts and going out of his way to accommodate her tastes are all ways a man shows his affection.
A man shows respect through more than just opening doors and pulling out chairs. His girlfriend's opinions matter to him, and he makes it clear by going out of his way to do things she enjoys or making compromises when he doesn't agree on something.
Men tend to show their love physically as opposed to verbally. Public displays of affection are a subtle way he can express his emotions. A man who loves his girlfriend is proud of her and her accomplishments. He introduces her to family and friends and makes sure to include her in all aspects of his life.