windows built-in remote login grants him the power

Windows built-in remote login is one of many ways that grant him power to access your computer. And a lot of software can let him view your screen desktop, or control your mouse cursor, even while you are using it w/o the necessity of knowing your password, for instance, VNC. As other suggested, re-install windows OS is the best way. Otherwise, there is no way to be certain, especially he is a SW developer. Back up your files, and ask help from some friends to re-install windows for you.