Don't back out! Therapy can be so wonderful and helpful. I don't know if that's true, though I have a feeling it isn't. But there are ways around it, even if it is recent. You can always say things like "hypothetically, what if I told you about ______. Would you need to report that/call the police?" And they can tell you before you tell them for real. Or if they don't have enough information to really make a reasonable report (e.g. you told them about a boy you knew who was assulted. No names, locations, dates, etc. There is nothing for them to report). Unfortunately, that's something I've had to discuss before. I talked about a friend's little brother who was abused by his parents but didn't use names or any identifying information so there was nothing the therapist could do anyway even if he felt it warrented reporting.
I'm not sure if this is relevant, but this was a hypothetical my therapist proposed to explain the reporting stuff:
If you tell them that you hate your neighbor and want to kill him and you're going to do it, you have a plan and everything, the therapist has to report that because your neighbor's life is in danger.
If you tell your therapst that you're really broken up because you just killed your neighbor, they can't/wouldn't report that because there is no one to keep safe anymore.
If this is YOUR abuse specifically, and you are a legal adult and it happened many years ago, there may be nothing they could do anyway because it's your information. Not 100% sure.
Best of luck to you!!