Mistakes does not recognise race, colour, creed, religion, age or your status/station in life. In short it does not care about your plus points or minus points as an individual. We all have made mistakes, some small, some larger and some very huge and no one can afford the claim that his/her mistake is the most terrible, mind blowing and massive in enormity or takes the place at the top of the heap. You have been worrying and circling around & around your mistake, of which the central theme is "My mistake/or mistakes are the worst of the worst, nobody can equal it". The thing is no one is exempted from making mistakes, certainly not you or I or all of humanity since history began 2012 years ago. The truth of the matter is we all have made mistakes and will continue to make mistakes regardless of whatever the situation/or circumstance be, the important thing is whether you want to stay down or pick yourself up, learn from it, let go and move on and this my friend, can only be done by you and you alone. As my respected associate has said, "Forgive yourself first".
Ps.Sorry In the light of what you have written I have only this to say (the words are not mine, it is from someone else) but the essence is just this "There is nobody so bad that He can't forgive and there is nobody so good that he does not need forgiveness".