When he broke up with you because he needed space, many years ago, that was the chance he took. You were forced to put the first bricks in the wall around your heart. There are consequences that may take years to play out, but every time there are consequences it is a chance to learn. It took a while, but he kept adding bricks to that wall and now he gets that chance!
I'm not sure (since you asked) that he isn't the man for you based on your paranoia and suspicions. Of course you can't shake it. Only time and consistency (so I hear! Still working on that stuff myself) can get you through that. Together. Two of you. not Three.
You SHOULD have walls around your heart right now. As others you trust have written, this is the point he has to "crawl over broken glass for you" [thanks to poster who gave me that image long ago]. The hardest part is having one ounce of faith at this point that they will do so... or are able.
My final "detachment" hurdle, was getting past that fear. I was actually more afraid for SB at that point. I knew I had the tools and ability to move on and create a wonderful life for myself and my family. SB was ashamed, depressed, and going through the motions. I didn't think he had it in him to fix the hearts he had broken. I had to accept that he would wake up one day and find himself the saddest man at the bottom of the bottle. I "knew" losing me would be the biggest mistake of his life. I "knew" that one day he'd realize it, but it'd be too late. I learned though, that whatever the consequences, I was powerless. Posters here helped me. He wasn't letting go. I dropped the rope. Long story. Endless nights. We were 1500 miles apart and he went darker than ever at first. His parents, our kids, our friends... all were calling me telling me his VM was full and he wasn't answering the phone. I even gave OW's # to his Dad so they could call and determine he was alive.
If he's the man for you, he'll do what it takes. If he does what it takes, then you figure out if you love the man this experience has shaped him into. You are right. The order is wrong. If he isn't willing to risk being alone to get the chance to have his family back...
Anyway.
Turns out, I underestimated the guy. Or his love for me. Or something. I told him what he needed to do, step one was break up with the girlfriend. I remember my H actually asking me for advice about how to tell her! UGH. We shake our heads in disbelief now, but back then I actually told him to lie to her and tell her he had to try for the sake of his kids. Yeah. I know. I'm luckier than I am smart sometimes. I should probably put a disclaimer on any advice I offer-- I'm way better at knowing what to do than doing it.
I told him I had faith in him (cough) and restrained myself from asking him each night if he'd told her yet. I spent a lot of time thinking up things I could find to tell him I'm proud of him about during the "process" and did my best to be understanding of how hard it was for him to hurt her. I was empathetic, I told him I understood how hurt she'd be, of COURSE she loves you... you are so lovable and "I remember how I felt when I thought I'd lost you." Just acted "as if" this was just what had to be done.
Everyone's timeline is different, I'm sure, but the DECISION was the key. The commitment to TRY to save our family.