What do I do when I have lost trust in my dentist?

It's really sad that this is happening.  It needs to be determined first whether the issue is with implants or with the fit of the temporary denture.  If you chose to go for a second opinion, you need to have some information about your surgery as to when was the surgery done, and most importantly which company brand implants are, and which teeth position they were used.  Without that information, it will be difficult or impossible for another dentist to get appropriate parts of the implants to help you and continue the case. Some parts of implants are recognizable, but still maybe difficult to tell for sure, but some smaller implant companies may have been unknown to other doctors.  Another thing, if Implant company provides a warranty then you may be required to use original implant parts on the top of the implants like even screws, otherwise the warranty may be void.     Your dentist should provide you the information about your implants, just like medical doctors do when for example they put any implants or a pacemaker inside ones body.  And  you need to keep that information for the rest of your life, so that if something happens down the line and you have moved or changed dentists it would be easy to fix if anything goes wrong with  them. As far as the charges are concerned, there are many different companies that make  implants and each have different warranty policies, as well as each dentist could be having different policies on implant management. So based on that your dentist is charging you a fee. 

You need to see a board certified oral and maxillofacial surgeon.  They are the most qualified doctors for dental implants.  Unqualified or poorly educated dentists who take a weekend course or 2 in dental implant placement often run into these problems.  Ask for a referral to a board certified oral and maxillofacial surgeon.  Sometimes "knockoff" cheap implants are used my non specialists to keep cost down but they are not guaranteed, sometimes the placement was incorrect, sometimes the denture was fabricated incorrectly and sometimes the patients immune response also is a factor.

the  problem with retained dentures , is a complex thing , because you have masticatory forces, and also you have many things involved, the prosthesis you have is temporary, it would be important to know what would be the final design, for you to get , so will be a good way of knowing what is the planned restoration.