As 1 John 1 puts it:

'If we confess our sins, he is faithful and just and will forgive us our sins and purify us from all unrighteousness.'

Or as 'The Message', a paraphrase, puts it:

'if we admit our sins—make a clean breast of them—he won't let us down; he'll be true to himself. He'll forgive our sins and purge us of all wrongdoing.'

whereas Satan is described as the accuser of the brethren - whether we see that as a literal person or merely symbolic. So the trick that works for me is to quote that whenever I start to let myself spiral into self-condemnation: after all, if God has forgiven me, who am I to condemn myself? As the counselling profession would describe it, it's about changing the tape recording that we play in our heads...

Welcome aboard. I hope you find this board as helpful as many others have over the years; it never ceases to amaze me how many come here deeply miserable and yet after a bit of time with us do experience a real change in attitude.