Next, Diotima asks Socrates why Love is love of beautiful things or of good things. Socrates replies that Love wants these things to become his own so that he will be happy. Diotima has Socrates agree that everyone always wants good things and happiness to be theirs forever. In that case, everyone would be a lover, but we only call certain people lovers. The reason is that, while everyone is in love, we only call a certain class of those in love "lovers." This is similar to the fact that while everyone who creates composes something, we would only call those who create music "composers."
So while love constitutes a desire for all kinds of good things and happiness, those who are money-makers, athletes, or philosophers are not normally called "lovers." Diotima dismisses the idea (that was put forth by Aristophanes) that lovers are in search of their other half, claiming instead that lovers love what is good. We would be willing to have limbs amputated if we thought they were diseased and bad, suggesting that we only want to be attached to what is good. Socrates and Diotima agree that love is the desire to have the good forever.
Diotima's next move is to ask in what way people pursue love. She cryptically claims that Love's function is "giving birth in beauty both in body and in mind." All people, she asserts, are pregnant in body and mind and naturally want to give birth when they reach a certain age. Sex is one means of giving birth, and it is through reproduction that we achieve immortality. This process is divine and therefore beautiful. Beauty is the goddess that presides over birth, allowing pregnant creatures to become pregnant and give birth when they are in contact with something beautiful. Thus, the object of love is not beauty, but reproduction in birth and beauty. Since love is the desire to have the good forever, we must desire immortality as well as the good, and in reproduction we come closest to immortality. All mortal things desire reproduction, and we see this even in birds and animals: they seek partners desperately, and will protect their young with their lives.
Diotima points out that though we talk about the "same person," we are not the same at all throughout our lives. Our body changes, as does our mind and our knowledge so that in old age we are nothing like what we were when we were young. We maintain ourselves in existence by replacing the old with the new, and so reproduction is just one further way of extending our lives.
Similarly, Diotima sees a drive for immortality in our search for honor. She suggests that Alcestis and Achilles would not have died for their lovers had they not known their heroism would be immortalized.
There are two ways men can become pregnant: in body and mind. Those who are pregnant in body seek out women with whom they can reproduce and create a bodily heir. Those who are pregnant in mind bring forth not bodies, but wisdom and other virtues. Thus, a man pregnant in mind will seek out one who is beautiful in mind as well as in body. The bond created between a man and a boy with whom he shares his wisdom is far stronger than a familial bond since ideas are more immortal than people. We worship poets like Homer and Hesiod and lawmakers like Lycurgus and Solon for the immortal "children" they have created from their minds.
You do not have to look outside you as everything is in your "self", everybody is the two energies (woman-man/yin-yang/...) and if you awaken your "opposite" you are "one", you are realized, totally happy. This is called e.g. in the Bible the Holy or Mystic Marriage. Also the alchemists describe it as "Coniunctio Oppositorum", the Philosopher's Stone, make Gold from Lead,... See the writings of the Mystics too. Etc.