Insecurity in a relationship due to love and decision-making

The speaker feels insecure in the relationship because they think love comes from one bucket, and if they give love to someone else, it has to come from their partner's bucket. They worry that the other person's relationship might grow to the point of choosing someone else. The partner feels that certain decisions made with the other person will affect them, and they don't understand the role the other person has in their partner's life. The partner wants to stay in the relationship but feels insecure about the situation.