Before reading this comment I strongly urge you and your mother both contact your local authorities, even if it's just so they have some form of record of the situation on paper. Also please do not delete anything that he has sent you for it may be used as evidence.

Firstly. Most photos taken from any phone are Geotagged. This is important because you maybe able to get his longitude and latitude from them. So on the dck pics that are most likely taken at his home you will have his home L&L and be able to use Google Earth to see exactly where it is and perhaps get an address. Also by him sending those dck pics you know his skin color and any information is useful information. Depending on device used even a date and time of those pictures were taken of you at work might be tagged on them. You could confront your boss and check video cameras of that time and see exactly who it is. Especially since you know his skin color. Speaking to police first is important due to the fact that you clearly do not know who this person is. Same thing goes for your mother.

Please use caution and use a smart head when going out. If you have troubles with any of the things I mentioned you can always comment on here if you would like assistance.

FYI: there might be a way of finding his real number through the textfree app, but I currently don't know of any.