I may be way off base here, because I don't have cats and never have, but, I know that at our SPCA they have a cat that is feral and they've had her for 3 years now. I know that when I sat on the floor over there that she decided I was ok if I ignored her and let her do the investigating. She eventually decided I was so OK that she climbed up in my lap. Please keep in mind that she had been there for 2 years when that happened.

I agree that you've obviously made progress. If the little guy is comfortable enough to lie on the kitty condo, he must be not nuts in the house now. Maybe if you sat outside of the room and just talked softly to him (without making eye contact) a few times a day, eventually he wouldn't be so freaked out and you could move forward. Like you said, he spent the first 5 months of his life in the wild and you've only had him for a short length of time. I would think that it may take a couple of years to get over it and perhaps he never will, but will enjoy the house enough that he can live in the house and have a long and happy life.

However, like Jo and Donna said, YOU are the one in the situation and have yourself and other cats to keep in mind. You need to do what's best for yourself and your other cats.