of course it is up to you and only you know your bf but i wanted to say something different.

if he is going to get it from you he will already have it. and if he does, there is no way to find out and even if you could there is no treatment so what your dr said is right - him knowing or not knowing will not change how you or your bf are medically treated.
if you are worried about him passing it to someone else in the future, everyone knows about the safe sex message and to have their pap smears so, they are adults, everyone knows that you can catch things from others and it is their responsibility to what they want with that info. I wouldn't tell just for that reason. There are many reasons why you may want to tell but it shouldn't be because of what might happen to someone else maybe sometime in the future

if you want to tell him, why hypothesis and guess about where you got it? you don't need to get into details of previous partners, gf or bf. you can tell him the truth that you have got it sometime in the past, but there is no way to tell from who. because although you are trying to put together some pieces to try and work out who it may have been, it is impossible to rule anyone out - even he could have given it to you, it is not impossible