As usual, people are taking verses out of context.
I John 3:9 means that if you truly have accepted Jesus Christ as your Saviour,
you are 'dead to sin'.

If you willfully reject God's offer of
redemption, and do not love, then you
are of the Devil.

Can you lose your Salvation? If you have
accepted Jesus Christ and then reject him
and lead a life of sin, sure.

There have been plenty of people who have asked for forgiveness and then asked again, after a period of Sin. Woe unto him who crucifies the Christ a second time.

But if you're an 'ordinary mortal' who fails from time, to time, or who occasionally blames G-d for your troubles, then, no. It's Men who fail G-d, not the
reverse.