This is a very informative post. I will like to commend you.
Like you pointed out, it's okay to sometimes put yourself first. We cannot actually love others more than we love yourself.
But when we think about ourselves only without considering the feelings of others is destructive. In little or no time, you end up alone as no one would want to associate with you.No man is an island and we need others to survive.
It's possible for someone who is egoistic to change. They must first accept that they have this problem and make conscious effort to change. They have to show more emphaty and be genuinely concerned about others.
It might sometimes mean making sacrifices when it's not convenient.