Love your wives (αγαπατε τας γυναικας). Present active imperative, "keep on loving." That is precisely the point.

Be not bitter (μη πικραινεσθε). Present middle imperative in prohibition: "Stop being bitter" or "do not have the habit of being bitter." This is the sin of husbands. Πικραινω is an old verb from πικρος (bitter). In N.T. only here and Revelation 8:11; Revelation 10:9. The bitter word rankles in the soul.