Oh no, you didn't fail, not at all, you just took a smaller step forward than you'd intended, and that's totally ok. Making a couple, or as many as necessary, attempts to test the waters is really very normal and does no harm to the overall value of telling him. I know it's hard when you intend to share and then don't go through with it, I've done this in therapy many times and know the frustration and let down and sense of failure all too well.
But they really aren't warranted. No harm has been done. There will be many more opportunities, and every little piece of disclosure, such as the fact that you're doing EMDR, is another piece of information into the overall puzzle for him at this point.
It just wasn't the right time, and that's ok. Try to give yourself a break and just "be" with this situation for now. You will know when the time is right, and if that isn't now, or for a while to come, then that's ok.
What's important is that you have quality time together and work on feeling safer and more secure in the relationship, because that's what will build you up to share what and when you need to.
Take it easy on yourself ok!
Maddog