This type of thing happens A LOT. It's not always with a boyfriend, often times its a relative and family members will choose sides. My guess is people don't want to believe someone they love and have invested time and resources could be so evil, because it reflects badly on them.
That's why you really need to watch who you let around your children, INCLUDING RELATIVES. I have several friends who have confided about their molestation to me, it was uncles, cousins, and close family friends.
If a child is acting like he/she doesn't like an adult, you better find out why. It doesn't always mean something has happened, but children have a great sense of intuition sometimes.