The goal is to attune to your partner, especially if they are not feeling positively. Be aware of their pain. Tune into their view of the situation and allow them to have their own way of looking at it versus trying to convert or persuade them to give up their view and see it your way. Turn toward their need, rather than turn away (dismiss them) or turn against (punish them for their opinion). Listen without becoming defensive. Call a time out if you get defensive as this is a killer for having necessary conversations!
And lastly, show some empathy. If they are in pain and you blow it off, dismiss it, minimize it or invalidate it- you have disconnection rather than connection.
You want to signal that when they are in pain, you are there for them, not that they are on their own! Not that your needs and self-interests are more important than your partner’s.
This is true of a friend, your ex and your current relationship.