No... it is not hopeless! Not at all! That's Satan talking to you and nothing more!
If you are Catholic, go to conefession.
But whatever you are I am assuming you are a Christian. Don't ever trust in your own sins more than God' mercy.
Look, the Bible speaks of blasphamy against the Holy Spirit being the unforgiveable sin. But the blasphamy against the Holy Spirit is not simply saying some stupid thing in the heat of the moment like some stupid movie about Dracula (sorry, I have that image stuck in my head). That's Hollywood crap. Sure, what you did was wrong and I am not trying to make it seem like it was nothing to worry about. But the sin against the HOly Spirit is precisely beleiving in your own sins more than God. That you have done something so horrible that not even he would forgive you. IN doing so, you are actively shoving God out of your life and actively denying the forgiveness he wishes to grant you. He will never lord his forgiveness onto you. He will give it freely... but you have to want it.
Here's the trick. Actually desiring it. desire is not just a simple feeling of "gee, I wish I had that". I mean, I can say, "I gee I wish I had a job" but if I jsut sit around all day and do nothign to actually find a job then... honestly, I don't want a job. I can say "Gee, I wish I weren't addicted to alchohol" but if the next time the temptation comes up for alcohol I give in like that and don't even care and tell myself "I'll take care of that tomorrow" then, I hate to say it but I really don't wish that.. in fact, my wish is that alcoholo control my life.
If you want to give yourself to God.. then do it! Pray fr forgiveness. It;s difficult if you are a protestant since you don't have confession as a sacrament. Even apart from the sacramental grace that is bestowed in the act of Absolution (as bestowed especially on the apostles in the Scriptures), it offers a psychological benefit in that it offers closure. It's easy for me to tell you to stop doubting your savlation and to ask forgiveness... but often, in circumstances like these, people have a hard time every TRULY forgiving themselves or recognizing that they are truly forgiven and carry it on their backs for their entire lives. That's dangerous living. iT wasn't until my fiance gave a full lifetime confession upon entering the (Orthodox) Chruch that she felt fully forgiven for all the nagging sins that haunted her throughout her life (even though she never let it show before that).
Also, if you often feel the need to blurt out things that you know you shouldn't but it's an urge to do the forbidden, you may want to talk to a therapist about this. Maybe this doesnt' describe you but if you do stuff like this every once in a while, to God or even to people (whereas most people might never or only once or twice in their life say something as serious as that) then you may want to look into that. Just a suggestion.
My prayers will be with you. Don't fear brother, God loves you and Satan does not EVER own your soul. He is NOT God's opposite.
John