I think there may be something going on with the bf but its more towards your fault.
I am not being mean but listen to me.
You said he changed. he obviously changed enough that you could see it.
When you constantly accused and fussed with him after he changed it may have drove him back to it.
"If you have negative thouhts negative things happen"
A one time that actually happened to me.(so you dont think Im sayin things without experience) A lotof people said I was tempermental, fussy and i had a lot of attitude. When I did change I could fight it for a while but people kept "attacking" me so I eventually went back to having an attitude but with more control because i actually started building it up inside.
Well anyways I think you should ride it out well at least until your "feeling" passes or the truth comes out. WHATEVER HAPPENS DON'T BE SURPRISED?