My advice is not to just use a stock phrase, "I understand," or "Sorry you feel that way", but to really listen and really try to understand. Then mean it when you say it.
Also, from the start, you would do well to establish the groundrule of not criticizing the other person. My H and I had a meeting like that when we were having trouble and ended up creating an ugly scene at a restaurant when it turned into him just listing all the stuff he hated about me. It is better to go with I feel whatever, such as "I feel alone with all the responsibility" instead of "You never help".
