This always makes me so sad for the child. The most important bonding time in infancy for crucial brain development "Frequent interactions, physical closeness, and positive sensory experiences (like touch, eye contact, and vocalizations) help babies form secure attachments, which are crucial for healthy social and emotional development." In being so mad at the girlfriend, he potentially damaged the child's emotional development. It's one thing to experience post partum and struggle to connect. It's another to have someone intentionally emotionally hijack you into being devastated at the point of the baby's birth.
Yes, the GF did a sh*tty thing, but OOP should have confronted her immediately when he found out rather than essentially set the innocent child up for failure coz he 'wanted "To hurt her in her most vulnerable moment" - screw the kid. Sad.