they should have adopted and severed his parental rights. he is an idiot
Note that some of the commenters are taling about what are the birthmother's feelings now, is she lesbian or straight, and "did the sperm donor choose to be a father" . Who the heck cares about "what she feels" or "when did he choose" or "whoever/whatever they now want or are now attracted to" etc. etc.
Obligations are obligations. Duties are duties. They do not depend on your on-and-off feelings. Children have rights which are natural, are imprinted in the bodies and minds, and are necessary for their life-long-flourishing.
#1 in the list of rights is, of course, the right to life = the right to just go on living, not to be assaulted, terminated, or murdered.
But right #2 is closely akin to it, and this is: the right to the support, provision, and nurturance of your natural father and mother.
That's what sex, love, and marriage are supposed to be about: the commitment of one man and one woman to each other and to the children born to them. They have the duty to acknowledge the child as bone-of-their-bone and flesh-of-their-flesh, to love and care for their child as such, because this is what every child needs to humanly flourish.
Pack up your "I feel" and "I want" and store it with the rest of your kindergarten memorabilia. An adult says: "The child's needs come before my feelings and wants."
Basic.