I'm afraid of conflict arising between my husband and me, so I pretend not to know about his mistress.
Literal
Husband [with-との] between [at-に] waves-wind [subject-が] stands [nominalizer-の] [subject-が] frightening, lover [possessive-の] existence [topic-は] not-knowing pretense [object-を] am-doing.
波風が立つ (waves and wind rise) is an idiom for conflict or discord arising. 知らない振りをする (pretend not to know) is a common set phrase. 愛人 (lover/mistress) is direct. The が between clauses links fear to its behavioral consequence. A emotionally charged confession.