If i had a chlamydia, gonorrhea and trich test in december, a year after possible exposure and haven't had sex since, can i trust the negative results?

I would: If your test was negative a year after last exposure it is negative for the germs tested. It doesn't mean you never were exposed, it means they are not present now and you would not be either contagious or brewing consequences of untreated disease. Syphilis is one STD not mentioned that can remain hidden for years with few if any symptoms as can many strains of HPV.

Yes: However, you should be aware that other sexually transmitted infections (STI) are also possible. If you do not have symptoms, then you should be fine. But if you're having any unusual discharge, blistering rash, or any concerning rash, or any other symptoms then other STI should be ruled out - if this is your concern.