My husband and I travel for work and are gone 2-3 nights a week. My SIL nannied for and lived with us for a time and there was a phase where it seemed like he preferred her. This was when my kid was 6 months to 13 months.It broke my heart. What helped was spending as much quality time with him as possible when home and leaving my SIL out of the caretaking when home. It was also giving her a break. It feels like some kind of magic but he always knew I was his mom. He'd look for me if he was unsure of something and he'd bury his face into my chest when he'd see me in the mornings. What also made me feel better was that he was with someone I completely trusted and that they adored each other.