They part, not to meet again for years, and never do resume their passionate affair.
They start a passionate affair and have sexual relations on a regular basis.
Two writers who once had a passionate affair meet years later.
They had a passionate affair from which she became pregnant.
For a year they have a passionate affair and everything is great.
On the night of their first meeting, she and B begin a passionate affair.
Their meeting immediately led to a passionate affair, and soon after to marriage.
This leads to a passionate secret affair between the two of them.
Of course, from your angle a brief, passionate little affair with no future might be just what you'd like.
Their days are the same as they always were, but at night the couple conduct a wildly passionate affair.