Pretty sure the only unforgivable sin in Christianity is to reject Christ as Savior.
as to degrees of sin, this is interesting (from biblebb.com John MacArthur)
Question
Are there degrees of sin, as far as...I’m thinking of lusting in your heart verses adultery?
Answer
Well, I think we would have to say that there are degrees of sin, yes. Just from the practical standpoint. I may entertain a thought of sin briefly; I may entertain that thought at length; I may allow that thought to become a deed; I may allow that deed to become a habit. So there would certainly be degrees of sin, and the Lord would say, the first time you have the thought deal with it then, and if you continue to have it, deal with it, and if you start to do the act, deal with it, and if its become a habit, deal with it. I mean at any point in the process the Lord would want us to halt it and not carry it to the next degree, to the next expression.
So, yes I believe there are degrees of sin. I believe sins of thought are an abomination to God, because any iniquity no matter how small abominates God. But, from the standpoint of practicality God will bless you if you cease from your sinning. God, I’m sure would be grateful if the thought of sin never became the act of sin, if it was dealt with at the point of the thought. Do you understand what I’m saying? You can’t just say, "Well, I thought the thought; I might as well do the deed! I did the deed I might as well make it a habit." I don’t think so. I don’t think so. So, God would be satisfied if you just stopped over here, and not convince yourself that because you thought the thought you’re as good as done the deed, and you might as well just let it run its course. No.
There’s another component to that, and I think it is perhaps worth mentioning. And that is in Hebrews 10, and here is a specific sin that certainly brings about a severer degree of punishment. Hebrews chapter 10, verse 29, “How much severer punishment, do you think he will deserve who has trampled under foot the Son of God, and has regarded as unclean the blood of the covenant by which he was sanctified, and has insulted the Spirit of grace?” What’s he saying? Well, all those who aren’t saved go to hell. All those who do not come to God through Jesus Christ will go to hell. But, the hottest hell and the severest punishment is reserved for those who knew, the most fully, the gospel and trampled on it. If a person rejects God, never hears the gospel, doesn’t live up to the light they have, is indicted on the basis of Romans, chapter 1, they will suffer punishment. But it won’t be like the punishment of one who has come to understand the gospel, come to understand what Christ did, who he was, fully understand that and trample him under his feet. That person will suffer the greater punishment.
So I think there are degrees of sin from the practical standpoint, and there are definitely degrees of punishment, which would reflect back on the level of one’s sin. So I think the answer to that question is, yes. I think what God would want you to do in your life is to cease at whatever degree you have reached, and not let it go anymore beyond that. A wonderful truth is that God forgives that sin, and God wipes out and blots away the past and remembers it no more. So the sooner you cease, the sooner it’s forgotten
