I can speak from experience that writing an apology can be very powerful. Even if your W receives it as manipulative (mine did), going through the process of putting myself in my W's shoes and empathizing with how my actions made her feel made me realize, finally, the huge role I played in the demise of our relationship.
It probably took me about 7 or 8 hours over a few days to finally get it, but once I did, it really opened my eyes.
Just remember, the apology is about the other person and how YOU made them feel. Don't rationalize your behavior or talk about your good intentions with your actions. It's about how your actions made the other person feel, not about how you wanted your actions to make them feel.
BD
My latest
Me: 36 W: 35 2 D: 9 and 5 T: 16 years M: 12 10/4/06: Bomb 10/5/06: Ended A 4/22/07: ILYBNILWY