that's a painful situation, it's hard not to feel like a failure too...  Only time will help you.

Critical Advice: 

1.  Don't talk badly about your wife to your kids
2.  Pay extra attention to your kids, especially your younger one. They need to know you
     are not divorcing them too.   It's a critical time make sure they do not feel abandoned.

Sometimes things that seem bad at the time, turn out to be blessings.  You are not responsible
for your wife's happiness. - that's an inside job.  Yes, I've had divorce therapy. :)

Paddle your ass off!