Or, putting it in another envelope, addressing it to OW, and letting her open it and read it!
That's my vote!
Aver, If I were you I'd put it away somewhere, and one day when you're ready, if you are still interested, you can read it.
I just think you have done so much work to be over him, why rip the wound open again. If you are totally obsessing, why don't you ask your C, and maybe read it with her?
Don't you think even it it did beg you to give him another chance, would you rush right back? Don't you think you'd proceed cautiously, knowing what you do about him now.
I've been harping on how hard you've been on youself for months, so I think you should pitch/hide the letter.
But the choice is yours. Whatever you decide, you are going to be just fine! Great in fact! ! I know it, you know it, your RL friends know it. You are strong, no matter what garbage he may throw your way.