Someone here told me something very valuable: Enjoy the interaction. Hug him with open arms. Don't initiate anything and let him take the lead, but do what your heart tells you. Remember, you can't believe what they say, but you can believe actions, 50% of them. Really it's the actions of my H that keep my in DB fighting mode.
I think you have good reason to be optimistic but yet still cautious. And I don't mean be cautious because he's going to bail, but cautious to not overwhelm him. Until he says outright "We are together again" either to you or someone else, assume he's still working things out in his head.
DO NOT GET INTO A CONVERSATION WHERE YOU ACCUSE HIM OF HIS BROTHER'S SINS. It's just not fair. Chances are, he probably knew his brother was cheating, but there's nothing he can do about it and he probably thinks if you know about it then you're going to assume H is cheating on you too. I don't know why, but I don't think your H is cheating on you. He may flirt, he may "hit" on women, but who cares? Don't men smile at you sometimes? As a matter of fact I went to play tennis last night and some guy hit on me! I can't wear jewelry when I'm playing so I don't have my rings on. The even more amazing thing is that he was wearing his RING!! And to be honest, completely harmless because I can't even remember what the dude looks like now and I bet it's the same for him.
H is not cheating on you. H is not cheating on you. H is not cheating on you.
He may have had a brain fart and thought he wanted to date other women, but I think you've been doing such a great job that he has changed his mind and just hasn't figured out how to say it to you because he was such an A$$ before. But he'll get there. You stay the course and don't initiate and just enjoy the interaction.
Maybe keep the intrigue going by not answering one phone call. That's up to you but you are doing great. This is back on track just give him some time to work it all out. And you never know, in his opinion you both might already be back together and he expects you know now that via mind reading.
You are doing so so well!