Was the original plan ever?...

Because he'd be a total moron to not realize he was wrong in hurting her at least.

I think Brock was now away from whatever situation he and Reba were in, and had the chance to think about it clearly and came to realize it wasn't as bad as he'd felt it was at the time. This isn't uncommon for people.

Plus, while he did love BJ, he did know she was cuckoo (and there were times you saw him grimacing at some of the things she said/did), and Reba was more grounded. After awhile, that had to get tiring.

Plus, the kids. No matter what else, he did love his kids, and he was probably thinking that his whole divorcing their mom to marry somebody else didn't do them any favors--Cheyenne being the most obvious, having got pregnant while he and Reba were separated, and that probably really hit him hard. He may have felt if he and Reba hadn't been having their issues, they would have been keeping a better eye on Cheyenne together. And while he wasn't living far away (around the corner, in later episodes), it wasn't the same as sitting down to dinner with them every night, saying goodnight to them, or good morning, or just casually walking by them and seeing them doing homework or playing a video game or whatever--now some effort had to be made for those little things.

Because Brock is a quitter and a coward. When something isn't perfect he wants to run and hide behind something else.

I have to re-watch this episode- I didn't get that interpretation at all. I just assumed that they were willing to do that hence neither of them knew who the other one was while they were engaging in their game of poker.