1) Not sad at all...your reaction is perfectly normal as you may be just a teenyweeny bit unsure of how they will react. I'd say have a chat with them...sounds simple I know but openly talking with them and broaching the subject when both are in a relaxed mood will help (even though you will probably be on pins and needles -there's a pun in there somewhere I'm sure of it!!)
2) Maybe dont go into too much detail to start with and just talk them through your feelings....there will be loads of questions like 'why didnt you tell me this before' or 'do you talk to anyone else about this' so be prepared to have to give some explenation..who knows your other half may actually enjoy that you have confided in them...I know many folks keep something like this hidden away!!
3) Clearly this is a bige side of your life so its only understandable that you didnt share earlier because of the negative sterotypes that surround this.
...please keep us posted if you are able to, as to how you get on...