I'm sorry it didn't work out - I really hoped your 'bonding' would go better than ours did.
George was happier with the girls next door than he was on his own - once he had assured himself that Zara couldn't get through! It took her nearly a week to stop cracking teeth at him through the bars. It unsettled the bond between Zara and Louise for a day or so. It was like Louise couldn't get over Zara putting a blocker on things because she took a fancy to George, and there was a lot of pee spraying and back leg kicking when Zara went up to her! But things did settle back down.
George has now found a friend to live with. We got a call from a lady who we had a 'last piggy' from years back, asking if we were in the market for a lone female last week. After the recent bonding traumas I was in two minds but after a couple of calls we decided to give Flora a try on a fit-or-return basis, because of course she had to like George, George had to like her, and Zara had to not kick off about it all. I'm not sure George was entirely convinced: if Louise was a Green and Zara was a Red (and how!) then Flora is Amber. She's 2 and quite a little girl and after a week it looks like George is dominant (although barely, I mean it's George, and he's wiping pee off his face every day) which is good for us as when the weather improves and they go outside she'll hopefully follow his lead and he's a safe pair of paws.
If you do social media it might be worth putting out feelers for any lone sows locally? People can be glad they're off their hands sometimes.