I hate to say this, and I'm going to get downvoted into the earth's fiery core, but maybe couples therapy is in order? Everyone is going to tell you to gym up, etc. and I have often given that speech myself, but to play devil's advocate for a moment (bear with me here):
I cheated once and only once, in my early twenties. I slept with an old friend when we both ended up back in our home town and ran into each other by chance. It was a horrible mistake and afterwards we felt like total shit. I hated myself-- I was cheating garbage!
My SO had no idea; to her, we had a terrific relationship. But her father had cheated on her mom and infidelity was my SO's bogeyman. So, being the slime that I was, I cowardly decided to not say anything. To be totally honest, I felt I deserved the guilt and she deserved to be as happy as I could make her.
And you know what? For a year the silence that I kept was the most decent thing about me. I know that sounds messed-up, but in that time I treated my SO like a goddess. I was constantly paying penance: flowers, gifts, aggressively-high levels of support, encouragement and affirmations. She wasn't an easy person to be with, but I was eternally patient with her and always let her have her way. Who was I to say anything? I was scum. She faked her orgasms? No problem. She told me she didn't like my friends? They were gone. She hid a terminated pregnancy from me and I said nothing. I deserved it all.
Inwardly, I was a nest of snakes-- I felt like shit about myself and every time I looked at my girlfriend and felt love swell up in me, it came with a surge of self-resentment. One day, I couldn't take the guilt and did the shittiest thing yet: I confessed.
People will argue that honesty is the best policy, but you know what? It's not that simple. My SO had a great relationship; as far as she knew, it was the best. All the truth did was hurt her. All I did was unburden myself by dumping it on her. I never intended to cheat again, I had definitely learned my lesson. I knew I wasn't the kind of person who could just do something like that and live with it. At that point, what good did the truth do?
She forgave me, but it wasn't the same. There was distance and scars. We dated for years afterward-- we lost what we had but we found other worthwhile reasons to be together (until the night I tried to propose and she confessed to having an affair with my best friend, but that's what I get, right?).
My rambling, over-sharing point is this: your husband did a shitty thing, but he may not be a shitty person. Concealing the truth might not necessarily be an act of cowardice-- it might be him understanding that you don't deserve this pain and heartbreak, especially if this truly was a one-time thing, which in your case it may very well be.
If this incident is uncharacteristic of him but is apparently standard SOP for your former bestie? Maybe you gave a second chance to the wrong person. He may be like I was: totally remorseful, wracked with guilt, overreaching for atonement, but also ready to own up despite hiding the truth. You were willing to give your best friend another chance, but not the man you love? Dude, marriage is a lifelong thing and if you think the happy couples you see around you haven't dealt with this same bullshit and worse and worked through it, then you don't know what's it's really like being tethered to another person until one of you dies. If you miss him and there's still reasons to be together and he's willing to put in the extra effort to earn back your affection and trust? Give it a shot. It can't hurt; give it some time and if it doesn't work, then you can always split. Good luck.