This is what imprinting is
Biological imprinting is defined as the process by which an animal, usually just after birth or hatching, attaches itself to another animal of its own kind or to a substitute object identified as its parent. In the Twilight series, imprinting is an involuntary mechanism by which Quileute shape-shifters find their soul-mates. When one of the pack members imprints on someone, there is a one way bonding that happens. The pack member from that point on is committed to the protection and happiness of the person on whom they've imprinted. Jake explains it to Bella thusly: It's not like love at first sight, really. It's more like... gravity moves.... suddenly. It's not the earth holding you here anymore, she does.... You become whatever she needs you to be, whether that's a protector, or a lover, or a friend.