Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) said concerning this saying of Allah Almighty, "And you will never be able to be just between wives, even if you strive (to do so)" [Surah al-Nisa: 129]: What is meant by this is love and sexual intercourse.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب القسم والنشوز / 14740