There is no such thing as an Ex-Christian. God does not give salvation to
some one and take it back. Since he has foreknowledge, he knows if and when
you were going to back out. So if you are not a Christian now, you never were.
Judas Iscariot was as close to Jesus as the rest of the apostles but he was
just going through the motions as you may have been. Maybe that's why you
gave up because it really wasn't in you to begin with.
The bible speaks of those that were once enlightened and turn away. It also says
in those cases it is impossible to renew them again. (Hebrews 6)
It also says that those that have been exposed to the truth and have participated,
then turn away, their punishment will be worse because they knew better.
In James it says, "A double minded man is unstable in all his ways."
In case you weren't saved in the first place, you should ask Jesus to forgive you
of your sins and to come into your life, then ask him to turn you into a believer.
Repeat Romans 10:9,10 out loud and mean it in your heart, then you can be sure
for God looks at the heart and he already knows in advance if you are for real or not.