what is love

I have been thinking a lot about love. What is love? What does it really mean to love someone? Why have we let society push us to believe love can only be between two people?
Once upon a time a great man taught the world to love, and to love everyone. Yet, society and standards today teach us we can only love one person at a time and we must choose only that one person to love and stay with "til death do us part."
I do not believe I have ever experienced true real love, the kind that is selfless, caring, giving, and open. That is the point of this ramble, open love. Why is when we do love someone we feel we must hide that love? Why can the love not be open? Why do those who are important in our lives feel threatened and jealous of the love we have for others? If love had jealousy and pride, it is not love.
I have come to believe that love, in its truest form is completely unconditional. Yes, you can get mad and irritated and upset with the person, but you never stop loving them, not for a moment. Occasionally, you realize they do things just to hurt you and you decide you must walk away from that pain, but you never stop loving them, at least I do not.
Back to my main point, why can we as people and a society not learn to love and to be happy for love when it exists for those we already love. In society, due to diseases, I would not want the person I am physically intimate to be out screwing other people all the time. However, if the person I love and am intimate with was mature enough to come forward and tell me they found a love in another person and that love brings them joy, then I would be joyful for them. Dealing with relationships in a manner in which we just want to see each other happy, where we can love and be loved instead of being bitter and finding hate, would it not make our society a much better place.
If I found love in another person, I would  not want my significant other or theirs to be upset about the feelings or the intimacy shared. I would want them to find joy in the happiness we found together. I would also want them to understand in the love I speak of, I do not want to be selfish and take something away from someone else but rather I want to share and to grow the love and respect. I want to be caring and considerate of the relationships already in place. I want to grow relationships from those and become a stronger, more loving unit for all involved.
The hardest part: I am happy for other peoples happiness. I am happy when others find love. I can still love someone who loves someone else. I do not appreciate when people feel the need to lie or sneak or withhold information about their feelings for others. Even more so, when I become hurt for being lied to and feeling I was taken advantage of, I do not appreciate being told what a horrible person I am or how I am so much worse than they imagined. The love is still there. It still exists. It is pure and good and true. My trust, that is different, because there is so very little I trust anymore so to have that broken because of games; that is why I was ignorant. I was stupid to believe others could be as open to the idea of love, real love, the way I am. I know there are others out there, but they are so rare and so few and far between.
(Apologies for the rough version of this rant, my mind is not necessarily focused as it typically is due to exhaustion)