Ask your partner how they slept, how their day was, about work, what's on their mind, why they've been quiet, why they are being sensitive, what they'd like to eat, and where they'd like to go; make it a habit. Never let them feel unseen, unheard, or ignored.
Its so different from open relationships too. I know ppl like to believe that open relationships are the same but theres really such a major difference between an open relationship and a coping relationship.