You could have lost all respect from your ex if you had cheated behind your ex's back.
However, all is not lost and you could surely regain the respect of your ex by following these tips.
Stay out of sight for some time.
Since you would have turned into a scumbag in the eyes of your ex, it would be wise to stay out of sight for some time.
This will allow all the anger melt away from within your ex.
Use this time to think on ways to gain back your lost love and also get an absolute body and mental makeover so as to make it difficult for your ex to remain angry at you.
Apologize when you return.
The first move that you should make upon returning back is to contact your ex in person and apologize.
If your ex is still livid then you should write a letter of apology.
You will not only have to apologize but also prove to your ex as to the steps that you plan to take so that such a mistake is never repeated again in future.
Prove your worth to your ex.
You should now divert all your attention on getting your own life back in order.
Prove to your ex that you can stick to your word.
Get back into your work routine and refrain from flirting forever.
Get into an exercise routine to divert your mind from thinking repeatedly about the breakup.
Let common friends observe the new and dedicated you since they will soon inform your ex about the positive changes happening within you after the breakup.
Wait for your ex to make the move.
Do not try to contact your ex repeatedly for a reunion.
Instead, stay focused on your own sin-free life.
Your ex will surely observe your each move and once he/she is convinced that you have genuinely repented then it will be just a matter of time before he/she approaches you with forgiveness in his/her heart.
Make sure that you realize the importance of this second chance and remain faithful to your ex for life.