Hi! For me simply relationship with another person. Because we can't do it all by ourselves! And as their would be all kinds of relationships then would be all kinds of love. It you are referring to just romantic love I would say we naturally reach out for the security we want in pair bonding which can hopefully lead to long-term relationships and children, family, community. But for that to work responsibility becomes necessary. If we are unwilling or unable to think and act responsibly well then the love we feel for one another remains in a very embryonic state and does not lead to any deeper personal fulfillment.
You seem to be confusing different quantities. I can love someone I don't respect or trust. For whatever good I happen to derive from the relationship. Is just that under those conditions well of course it is not going to go very far. Someone we respect and trust we love as well but might not be romantic or sexual or caring love or the kind of enjoyable relationship which brings people closer together.
For me, love is neither an illusion or delusion but rather very real. The true meaning of love has been corrupted in the common usage of our English language and society. Most often, love is confused with infatuation - that elated, "high" feeling we get when we "fall in love." This kind of "love" is something that lasts usually a year or less, and unless replaced by true love, results in broken relationships and the terrible aftermath that sometimes accompanies it. :)