I believe that this applies only if you purchase books directly from Harlequin. Harlequin books purchased from other online stores should be unaffected.
Their announcement says that they are changing providers. Their
online store is currently provided by OverDrive, and it looks much the same as the websites of OverDrive libraries.
They don't say who the new provider will be. It will be interesting to find out. They also don't mention it, but it is most likely the new store provider will not support ADE since that is expensive.