This is the Psychologist in me talking...
I think the problem is that Brad found his brother the perfect wife and that romance was exactly the type Brad described wanting - instant fireworks, knowing immediately that she was the girl. I don't think Brad needed to have love that way until Chad got it that way. If Chad had been best friends with his wife and fallen in love with her over 3 years, that's who Brad would want to fall in love. We would have heard him saying "I know I can't be in love, because love isn't something that happens in 6 weeks, it takes years, you have to be good friends first."
Brad has probably always wanted the exact same things as his brother - the same stuff, the same accomplishments, the same approval. I don't see him as the type to one-up his brother. I think the fact that they're business partners means that he wants to be like him, not better than him. Some twins are competitive, some find comfort in always maintaining symmetry.
At 35, after Chad had been unable to find a wife him, Brad decided to go on The Bachelor and get that big romance. Now that I've seen the whole thing, I do think he was sincerely trying to find THE girl.
Brad desperately wanted it to be Sheena because then the universe would have been balanced since Chadpicked her for him. I think that really would have made him happy and we saw him try really hard to love her, but unfortunately, Sheena's family sent him running scared. He couldn't blame Chad, because it wasn't Sheena, but her family that wasn't right. After meeting Brad's mommy, I think Brad knew that Sheena's mom would have driven his mom nuts and it was a big NO for that reason.
Once Sheena was gone, Brad focused on the other 2 and he really tried to convince himself there were feelings and those fireworks. I think that's exactly why he repeatedly made affirmations out loud - not to string the girls along, but to convince himself! That's why up until the last minute he said the them. He was really trying up until the last minute and he said tonight that he tried but there was something missing.
Brad didn't want to return home without a fiancee, because he's tired of not having what Chad has. However, at the last minute, he realized picking Deanna = settling for less than Chad.
The truth is, a lot of very happy couples marry without it being an instant head over heels thing. Some of the best married couples are friends who fall in love slowly over time. That's what Deanna wanted to try. She didn't need Brad to instantly fall in love with her, she wanted to see if they could walk away from the spotlight and fall in love off camera. She was saying it's only been 6 weeks and you say you care deeply about me, why isn't it logical that we keep dating?? Unfortunately Brad is too restricted by his Chad Equality Issue to do that. Agreeing to 'wait and see if love blooms' is admitting that he'd settle for less than his brother got. No can do.
I find it extremely illogical that Brad couldn't have a friendly dinner off camera with Deanna and not let things end badly. Why make it so they both leave feeling emotional and heartbroken (Brad's words) when there is nothing stopping them from talking until there's closure? I don't think Deanna is an unreasonable person. I think she just didn't want to be told "I care so much about you...but I never want to see you again" because it's a sucky way to treat a person who has been nothing but gracious to you. A person who opened her home and shared photos of her dead mother, not some bitch he met in a bar that never showed him kindness.
I'm glad Brad admitted he has some issues!