It was just a childhood game, a act of curiosity, most people would of done it as a child, some wouldn't remember it aswell as others, some wouldn't even mention it anyway.
and of course at the time you wouldn't of known what you were doing was wrong, so therefore you shouldn't think any less of yourself.
Naturally if this past now makes you feel sick and dirty, then its normal for you to be put off by sexual activity.
I think seeing a psychiatrist should be a last choice, counselling would be your best option right now, of course you may prefer to see a female counsellor but i dont know that.
As for your boyfriend, if its that much of a issue for you then i see no harm in telling him, but only if you want to tell him, if hes as caring and lovely as you suggest then he will fully understand the situation.
Sorry if it sounds like im rambling on abit, hope my advice helps.