well well, 3treefrogs you have brought up a very interesting post, and one i don't have the answers for but can give you some thoughts.
as far as talking to psychiatrist or counselor, my thought would be that if you cant who are you going to talk to, these people have studied very hard and you may be surprised that they might have dealt with the same subject matter on numerous occasions with people in your same or similar circumstance, so why not talk to them,isn't there a policy of confidentiality? But as JustinOK said beware of the legalities and such.
now i don't know what the taboo stuff is, but my question would be, taboo to who? weren't some going to burn Elvis for shaking his hips, and things that are taboo here in Australia might not be elsewhere in the world.
the fact that your conversations with your online friendship/ confidant are strained brings me to remember the similar situation online many years back when i said things i wish i didnt and it was strange there for a while, but after some time it got better and we both simmered down and our freindship continued, a breather can sometimes help after both parties have had time to reflect on things.. but in saying that i have had things go bad as well, so i wish you the best and hope you get back to a good place with your friend and have that support and mutual understanding.
i also think rocking up to the local sexual health center might be a good idea in regards to talking about the taboo stuff, from my experience people there are very helpful and can refer you to the right people, and they are down with youngsters and the hip cool gang in regards to the stuff that is going on, eg nothing will surprise them.
best of luck