All the quotes are correct, and all of them are directly related. If you agree with one, you have to agree with all of them.
The typical idea for the strongest love is considered by many that one person dies for another; in other words, sacrifice. Love is a verb, not a noun. It isn't a feeling or an emotion; that's just hormones. True love doesn't exist between "lovers" so much as it does between parents and children; and such love is almost impossible to find around here these days.
For true love is unconditional, it means, "I love you... no matter what."
It is not, "I love you... because you're beautiful." or, "I love you... because [insert anything you want to say]".
So the married and dating couples can say that, well, it has a harder meaning than just being romantic. Girls, imagine if your boyfriend/husband had sex with another woman? I don't care about what my sister said when I asked her (who answered, "Oh, he would never do that!"). Would you still love him? If you had a past relationship when you were cheated on, and you dumped the first guy, reconsider your thoughts.
Guys, if that girl of yours walked away from your dreams and imaginations to go and pursue something else, leaving you behind, would you still love her?
This is all vice-versa. But the idea remains. If your significant other burned your house, killed your cat, mother, sibling, or if your best friend had an affair with your spouse, would you still love them? If not, it isn't true love. Loving is about complete and total 100% you don't care what they do or how they act, or how they look. You don't even care what they look like on the inside. Even if your significant other turned into a crazed killer on the run, caught amnesia and didn't remember you anymore, or hit you or threatened you.
When you get two lovers like that together, the bond is truly inseparable. Take it from a story I'm writing for one of my books. A man obsesses over this woman ever since she graduated high school. He followed her and hung on her, lived for her, even went to bed with her once or twice, but she eventually got married and had children. Furious, the man stalked her husband and eventually threatened his life to her. He set her up to have an affair with him and for her husband to find out. He threatened to kill him as well.
So the woman divorced her husband and re-married the madman. Eventually, the husband finds out near the end, through all of his pain and sorrow, that she divorced him, left their children, and married another man who tormented her in bankruptcy and mad obsession because she loved her husband that much.
Would you love your spouse enough that you would forgive them if they left you for someone else or cheated on you? If not, then it was never true love to begin with.
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Now, this is the major reason I'm not going to marry. Because I believe the girl out there for me deserves to have someone else. I don't think I've met her yet, but I love her enough not to marry her. I have said elsewhere that I am genophobic, have the fear of sex. I'm also an exclusive pedophile, meaning I am sexually attracted to only young girls.
My wife, if we married, if she had true love for me, would suppress her needs for a sexual relationship because she knows that I have a particular distaste towards sex. And she would lay in bed and suffer because of me, and the thought hurts me. She's going to know that I don't appreciate her beauty, and if we had a son, he wouldn't be her own but most likely adopted.