If you maintain a feeling of compassion, loving kindness, then something automatically opens your inner door. Through that, you can communicate more easily with other people. And that feeling of warmth creates a kind of openness. You'll find that all human beings are just like you, so you'll be able to relate to them more easily. That gives you a spirit of friendship.
There are no limits on true self-giving. It is not just to those one likes that one makes the offering. This involves a love that issues from the very CENTER of the person's being, directed to the CENTER of the other person's being, a love that gives ALL that the person is in order to foster the other person's life, a love that is offered to EVERYONE, without exception and without condition. The love is not offered to people because they are one's friends; people become "friends" because one loves them.