"You don't know how I feel." We have said this. We've been told this. Like you, I know the experience of being misunderstood or have my feelings discarded. I have misunderstood others as well.
Some people are just not able to know how others feel. They have no theory of mind, and thus no compassion. Simply unable to imagine the mind or feelings of another person, we see this as we watch what they do.
To become more compassionate takes effort. First, I try to be aware of people's feelings and moods when I photograph them. This may mean listening instead of photographing. It might require putting the camera aside for a while. Compassion can mean returning at a better time when your portrait subject is feeling better. At times, we might have to work at a slower or faster pace to match the pace of our subject. It can lead to making a game of the photography process or giving control in a session to someone who objects to being photographed. Compassion always demands a change from self preoccupations to thinking of the needs of another person.
Compassion is not passion. While they may be two wheels on the same drive train of our mental energy, passion is more about the self and comes from inside. Compassion is about feeling for another and it's more often impelled from outside of us. It starts outside of us when another person is suffering, and we are moved to suffer along with them. Compassion is not altruism. It is not empathy.
Compassionate people are described as patient, kind, wise. I was not born with these traits, and I have to work at it, to practice to become more compassionate. I've found compassion an immense challenge. Often I find it hard to maintain compassion and transform it so it lasts.
Compassion Exercise: Keep a gratitude section in your diary or journal. I began to keep a gratitude journal in 2019, writing down all the things for which I am grateful.