I had always tried to do my best for my stepsons. The youngest was his momma's boy and she made it difficult for my husband and I to establish any real relationship with him. They divorced when he was 3. The older boy lived with us for awhile and we got along great... until I got pregnant with twins.  He started rebelling pretty hard during my last trimester and I was stressing pretty hard. After he tried running away, we decided it would be best for him to go back to his mom for awhile and we would revisit him coming back to our home after the twins were born. 
Fast forward about three years. He's been back with us for a year, my twins (both girls) are almost three, plus we have a newish baby boy.  Youngest stepson is visiting for the summer and then both boys go to their mom for a month before they both come back to stay with us. 
One night, one of my girls comes to our door crying hysterically. Her limited vocabulary at the time made it difficult to find out exactly what happened but we were able to make out that the youngest of the two boys had "put an owie on her butt".  We checked her over and couldn't see anything unusual. The boy in question was sound asleep. We made an appointment with her Dr the next day anyway. That got CPS involved.  Throughout all the questioning and exams, there was no conclusive evidence. 
The boys went to their mom and we tried to pick up the pieces of our family. After 3 weeks, we find out the oldest boy has been arrested for molesting a 9 year old girl. My husband and I go up for the hearing and he's sentenced to time in juvenile detention. He's 16 at this point.  
Because he was out of our state, visitation was difficult but my husband and I alternated our visits. He'd go up one month, I went the next. During one of these visits, I found out that he was the one who had molested my daughter, not his brother. And he had also molested her sister. 
I was devastated. Even now, 20 years later, I still feel like I was a crappy mom for not protecting my daughters from this evil.   I still have a ton of resentment toward my husband and I hate that because he's really a great man and he's been an awesome Dad to our 3 kids.   He's so torn between the love for his firstborn and the horrible things he did to our babies. 
But this one has burned me so many times. I didn't cut off ties with him until last year when I found out he'd been lying to people about his Dad and me. 
Now he wants to reestablish a relationship with his Dad and it has opened up a lot of wounds.  I'm just not feeling very mature about things right now
thanks for letting me vent