A good companion can give you comfort, love and support. There is no such rule that only human being can be our companion. But I believe it can be anything- your pet animals, a great book, a gadget or any other thing you are attached with mostly.
A companion is who, with whom you spend most of the time or travel with it. Who can give you comfort, accompany with your loneliness and give you time. When it comes to love, I think if you partner is your companion then it is the greatest paring.
If your partner is your companion then there must grow a good relationship between each other. As we used to share a lots of things with our partner, so being loved and getting support from them is great.
In general, who gives us company is the companion of us. But we often used to see people living with there family and they are not that much attached to each other. They are surely not companion to each other. They may stay under the same roof but may not share same thought or fail to comfort each other.
Love is the bounding that helps us to be with our companion. To have someone like this is very necessary in everyone's life. Without others love, support and comfort we can not life peacefully longer. We must make a good companion with others who we love most and want to spend more time.
A companion is whoever is close to you by physical association and other form of relationship like marriage and friendship.
A true companion ought to understand themselves to an extent to facilitate mutual camaraderie.