Holly, I'm sorry you're going through this, yet again. You know I've been there with my H. The second bomb was harder than the first one, in many ways.
First let me say this... no you are not acting as another bandaid. You are the real deal. OW is the bandaid. However, your H is not ready to be in a R with you. Maybe it's too hard. Maybe he's scared. Whatever the reason, he's not ready.
It was not a mistake to take him back, IMO. This was part of the process. He needed to go through this step. He wasn't happy wiht OW. He missed you. He came back to you. And once again, not happy. Maybe he misses OW (often the case with these folks). And if he goes back to her, he will once again realize that is not doing the trick.
Where does that leave him? Finding happiness and peace within HIM. He will reach the point (and maybe he already has) where he has no choice but to look within. This is all hard work. But he has to do it to find happiness.
Going dark is the way to go. Don't enable him. He may want to call you when he's feeling weak. Don't be there for him now. He needs to rely on himself when he's feeling weak.
All that said, you remember how much back & forth my H did, right? In fact, after the second bomb, he said, "Don't worry... I'll never come home again". And two months ago, he was back, and in therapy. Now that wasn't the end of his back and forths... but it was the beginning of his endless spinning that enabled him to finally break through and find peace and eventually becoming an active and engaged part of the family again.
You are doing ALL the right things. You are a strong woman!
Married 9 years Kids 5 and 6 Bomb 2006 H back and forth for a year M now back on track