I have never been heartbroken in a big way, so far in my life.
This means you might not have as good a well to draw from to write about heartbreak. Unless you are a sociopath, you have almost certainly experienced emotions, and you've probably experienced strong ones.
In fact, it's probably an emotion that drove you to ask this question. If I had to guess, I would say frustration brought you here.
All humans experience emotions (psychologically speaking). Good writers and creators might not have any greater depth of emotional experience than the majority of us, but they almost certainly have two skills related to emotions that not everyone has.
- They likely are very aware of the emotions they feel.
- They also have an awareness of the emotions that other people feel.
Those two skills are linked, and by fostering one, we also foster the other. In other words, if you want to understand how other people feel, you need to start to "listen" (internally) to how you feel. And if you want to better understand how you are feeling from moment to moment, you need to learn to be aware of how other people are communicating what they are feeling (often in non-verbal ways).
I will use sadness as an example. Deep sadness usually creates an involuntary, universal response in humans: we cry. We can easily tell when someone else is experiencing sadness if they are visibly crying. And similarly, if we feel like we might cry, a good bet is we are also feeling a deep sadness.
That's an easy one. There are other situations where the emotions at play are not so obvious. We might find ourselves yelling at someone without knowing exactly why. Clearly we must have been feeling an emotion, and probably a strong one. Were we angry? Frustrated? Confused? More likely some mixture of those and more. Teasing out those complex and subtle emotions and understanding them in ourselves and others helps make us effective creators of art (by "art" I mean any creative work, including music composition).
The best way to become more sensitive to the emotions that we and others are constantly feeling (and expressing) is to listen. We have to listen to ourselves and listen to others. But it's not so simple as merely being quiet and letting sounds cause our eardrums to move. We have to listen actively and pay careful attention.
One way to for us to listen to ourselves and our inner emotional journey is through writing, such as a diary or a journal. Much of that writing might be fairly mechanical (e.g., "I flew to California today"), but sooner or later (if we force ourselves to keep writing), we are all likely to digress into details that either explicitly or implicitly record our emotional state. It's easier for us to examine our own emotions when we have some distance from them, so reading about them later on helps with that.
Another way for us to listen to ourselves is through meditation. In meditation, we work to focus and remove mental distractions to better connect with our inner selves. Meditation as a broad concept does not have to involve sitting cross-legged in front of a yogi and imagining a vase being destroyed and re-assembled. Any practice that clears and focuses the mind, like long-distance running or painting, can help us open up to our inner selves.
To listen to others is more simple and also more difficult. Not only do we need to hear their words, but we also need to pay careful attention to their non-verbal communication. To effectively listen, we have to silence our own inner dialog and give our attention completely to the other person. With practice, you will find you are noticing many subtleties in how people express themselves. What we think people are feeling when we listen carefully may only be educated guesses, but that's good enough for showing people greater understanding in both life and art.
You and the people around you are constantly experiencing emotions. Many times in modern society we try to ignore and diminish our emotions because we believe they hinder our effective decision making and distract us from tasks that we must perform to keep our jobs or succeed in school or take care of the house. Even young children have already gone through rich emotional journeys by the time they learn to talk. They have loved their mothers, lost a pet or a toy, felt helpless and ignored and alone, and experienced the joy of their successes and praise of the people around them. But we don't stop going through those types of events and emotions when we are no longer children.
Those are some examples of universal feelings that we all experience essentially every day. Tapping into those emotions will also connect you to the rest of us.
I sit down to write music, and not one melody comes out from me that isn't similar to something that I have already heard before.
This is almost a separate question. You don't have this problem because of a lack of emotional experience. Everybody has this problem. Our problem, as composers, is that we are all intimately familiar with our strongest influences. That means we more easily recognize the works that we admire when we accidentally imitate them than anyone else ever will.
It sounds like you haven't found your process yet. Somehow you have to almost hypnotize yourself into finding this other side of your brain where you tap into your inner creativity. That makes it sound kind of mystical, but it doesn't have to be at all. I'm a very rational thinker with a degree in mathematics and a good head for logic. It's no wonder that my process for composing involves looking at shapes and patterns and mutating them and turning them around. I have a great memory and I often find myself accidentally imitating. But I don't throw out the imitation. I keep it and I make it mine. I change it, I change the rhythm, I invert the intervals, or just one interval, I change it from major to minor, or I just play it on a different instrument. I think a hallmark of an effective process is that it plays to your strengths. For me, I use my memory and logical abilities to steal from the music that I know and make it mine by applying semi-logical and mathematical processes to it until it's unrecognizable.
The way to find your process is through diligent practice and hard work. Keep writing. Go ahead and write something based on a melody you know you didn't invent. Who knows, you might state the melody, put some counterpoint to it, like the counterpoint, develop it, drop the original melody and then you've just made something new. No one can tell you what your process is, you have to find it. You have to make a journey of a thousand miles into the wilderness to find it, and those miles are composed of playing and searching and working on your own music, your own sounds, and your own rhythms.
You've been given a precious human birth, like the rest of us, and just like every composer who has ever lived, humble or great. You are going on an emotional journey through your life and through the lives of others, just like the rest of us and just like every composer who has ever lived, great or humble.
The distance between you and your voice and your art can be covered by diligent hard work. If you choose to love music, nurture it, care for it, and give yourself to it, you will find that the work is its own reward and before you know it you'll look back and not even know how you composed some of the melodies that you'll have written. I believe from the frustration that you probably felt when writing your question, you care deeply enough that you will make the journey.