To be fair... your question assumes that Jesus Christ exists and that being a Christian means you have a relationship with Him. If you assume that he does NOT exist, then being a Christian just means you THINK you have such a relationship. Steven fit that bill.
He doesn't have to say "I was never really a Christian". It's the OSAS crowd who needs to make that argument to remain sane.
II - You are, however, moving outside the bounds of "invincible ignorance". It may be time for a screen name change.
We could raffle off the rights to pick it?
If you THINK you have a relationship with someone you assume does NOT exist then you are crazy.
Steven fit that bill.
I'm not willing to go that far. ;^)
This isn't complicated:') You are either saved or you aren't. If you aren't you are lost. If you are and turn your back on Christ the consequences aren't limited to just you. You may have fire insurance but what about others that might be led astray? spouse, children, friends etc.