Honestly, I don't believe in true love. I believe that love is something affected by various external circumstances, therefore it can never be true or pure...
That said, I love this man. I don't know what it feels like to be 'in love' (really don't know what that even means) but I know I care about and look after this man like I do my close family (my mom and sis). Even if we are never in a serious relationship mode, I will want to be in his life for as long as we both have it.
You say you love this man and you care for him like you care for your family. But are you IN love with him? You say you don't want to be without him, so does this mean you have serious romantic feelings for him? Or you can't be without him like you wouldn't want to be without your father or close uncle? Seems like you haven't really figured out what you really feel for this man. If you haven't really thought past a year or two I think you're going to have a big surprise when you finally grow into yourself as a woman. You're only 21, and there's so much more about yourself you need to get to know. I think at this point in your life you should be "soul searching". Sounds so cliche but you'll know what I mean in about a year or two. Goodluck!