Love as a Condition

"Love is the condition in which the happiness of another person is essential to your own."

Heinlein

If your happiness is dependent on the well being and happiness of another's then you are loving someone else - as yourself. Their happiness and your happiness are interchangeable, because you are one. I'd go even farther than that and say that their happiness may be more important to you. Philippians 2:3 and 4 reads, "in humility consider others better than yourselves... each of you should look not only to your own interests, but also to the interests of others."