What to do about my long flat face? (Photo)

You have beautiful features and are being very hard on yourself.  If you do anything, make sure it's minimal and reversible if possible.  I would consider nothing more than fillers.  The way you talk about yourself so critically and "hate photos" concerns and saddens me. You gotta love yourself...

There are multiple treatment options available. For permanent results, I would recommend a combination of silicone cheek implants and chin reduction surgery. This will provide a more feminine appearance and improved balance to your facial features. Cheek fillers offer a temporary solution for your cheeks, but a reduction of your chin prominence will essentially shorten your face and therefore, add more balance.

Any flat face can be improved with one of three ways; moving the bones, augmenting the face with implant or fat injection. Those of trained in the craniofacial surgery suggest an appropriate operation based on many factors. I believe you have a very pretty face but if you want to improve it it should be done with the minimum risk and lowest cost which would be fat injection. A virtual or real consultation with an experienced plastic surgeon may help your decision.

When patients have a flat maxilla and a flat cheek profile, cheek implants offer a permanent solution to improve that area.  Fillers can be performed in the office setting for a temporary augmentation.  For many examples of cheek implants, please see the link and the video below

In trying to get more of a heart-shaped face in one that is vertically long, vertical chin reduction/reshaping would be a key component of it. Adding width at the cheek level would also be helpful as you have indicated and this largely requires arch expansion more than just frontal cheek augmentation alone. Whether this is done by injectable fillers, fat or special cheek-arch implants is up for discussion.