If you have some concern or suspicion that someone you love or someone that you are close to was abused as a child and you do not know what you should do, you should ask them. It is not an easy subject for a victim of childhood sexual abuse to talk about it but if you notice, some type of behavior or something about them that makes you think that, that might have been the case then there is a chance that it was.
It is also something that that individual is trying to talk about or trying to get out in some way, they just do not know how to do that themselves. If you are close to them and you feel that they trust you, you should ask them right up front, "Did something happen to you as a child?" or "Were you ever sexually abused as a child?" You can tell them that they can talk about with you. You can make them feel comfortable in discussing with you what happened.