I'm not sure what you expected. You held yourself out for judgement when you wrote the article. Sure, he is responsible for his part in what happened as he had unprotected sex with you. What you did was unethical. Not because you had sex with a married man, per se, but because you did so with the concealed intention of having a baby. The fact that he did nothing to protect himself from that occurring doesn't change that fact. If you are honest with yourself you would admit: you knew he didn't want to have a child with you. You took advantage of his poor judgement.

As you said, you aren't wrecking his marriage and you aren't forcing him to pay child support (yet, 18 years is a long time). There is something to be said for that. Still, he will be stuck living with the threat of you dropping in and ruining his life at any moment. He bears much of the responsibility for that. Had he wrote the article, I would have commented as such. However his fault is the lack of intentionality where your fault is characterized by it.