I've mentioned that Eric is skittish about emotions, but I don't think I've explained why.
A couple years before they approached me about falling into bed together, Gia and Eric met a girl named Jen. They both liked her very much and she liked them. Eric was especially fascinated by her sexually -- she was a hardcore masochist. She became their girlfriend. She and Gia were genuinely in love, while Eric said he loved her but didn't really see her as more than a fun time and a friend.
Jen found herself in a bad financial position and they invited her to move in with them. Jen... had some issues. She was bipolar and often unmedicated. She blew up over crazy things and was very insecure. She and Eric would go out on dates and she would expect romance from him. When she didn't get it, she got even more freaked out, naturally. Gia got nervous about their relationship and asked them to put sex on hold. They said ok, but then she found out that Eric had been doing very sexual things with Jen, just stopping short of penetration. Jen had truly thought this was fine, but Eric knew it wasn't. He was basically cheating on Gia, or at least violating her wishes.
Their marriage came to a major crisis. Gia thought seriously about leaving him. Jen moved out. They started each seeing Jen separately, rather than together. Things were particularly tortured between Jen and Eric. She was desperate, in love, hurting, he was miserable with guilt and with the realization that he hadn't even loved her in the way he'd said. He felt responsible for her pain and had a very hard time dragging himself away from the drama... both the drama that he'd caused and the drama that Jen naturally projected. Finally, he managed to break it off.
Gia and Jen at first tried to keep things going with the two of them, but it was impossible. Jen eventually moved away from the area and stopped talking to Gia completely... despite everything, the loss of that love and friendship wounded Gia deeply.
That's my secondhand recollection of the whole thing anyway.
Gia and Eric stayed away from poly after that and just worked on their marriage. They got past it all, though scars remained. Eric, in particular... having almost lost the center of his world, his marriage... having made a terrible, ugly mess of a relationship with the woman who had been his girlfriend... having lost the respect of more than one of our mutual friends... seems to have done the most to try to learn from the whole thing. He's brutally honest with himself and about his limitations and foibles. He's humbler, more communicative, more empathetic.
I was the first woman they approached for anything extramarital post-Jen. Gia and I fell into a dating relationship fairly quickly, and I was surprised to realize that she wanted me to be just "her" girlfriend not "their" girlfriend. I didn't know then that they'd previously made every mistake in the unicorn hunter's handbook, I just knew that they're dated a girl together before and it hadn't worked out.
It was Eric's firm contention when I tried to feel him out about a possible emotional connection more than a year ago that he doesn't love easily, doesn't know how to be romantic, doesn't want or need an emotional relationship outside of Gia. He said once that it's better to be "a minor villain in the first act" by letting someone know he's not in it for love, than to be the major bad guy at the end of the story by leading someone on.
So, you can see why I've held off.