The slow-warm read
The friction tends to arrive when a partner reads the slow-to-warm as rejection, or as a sign that the relationship has a problem. In trusting, the body doesn't open on a schedule. It opens when all the conditions are met, and the conditions are real, not arbitrary, and not easily summarized.
What helps
"There's no pressure. I'm not going anywhere." "Take whatever time you need." What helps: a partner who can hold steady through the slow-warm without making it mean anything about the relationship. Patience that doesn't feel like waiting-for-payoff. This reach is among the deepest available, but only inside a room you helped build.