Re: MRSA and Trichomonas
Flagyl kills Trichomonas pretty easily, so as long as you guys didn't have sex (unprotected or protected) while you were on therapy, you're both likely clear of it.
As for the MRSA...MRSA is drug resistant, yes, but that doesn't mean there aren't oral antibiotics which can treat it. Did your boyfriend have one abscess or more than one, and where exactly was it?
Community-acquired MRSA often presents in healthy people as multiple boils. It probably doesn't have much to do with the Trichomonas and was just bad luck they appeared at the same time. Unless your GP is familiar with MRSA, your boyfriend needs to get the abscess lanced, with or without concurrent active oral antibiotics if there was a lot of skin inflammation. After he's done treatment, he needs to go on what we call a "decolonization protocol" which is essentially baths, shampoos and oral antibiotics for a week to rid himself of the MRSA colonization.
Many people become recolonized, but 60% of people after being decolonized, won't have problems again.