["I'm finding it super hard to move on from my last relationship.", 'I know how that can be such a struggle.  How long has it been and why did it end?', "Thanks.  I messed it up by cheating on her.  It's been 5 months"]
Everyone makes mistakes, we live and learn I guess.  If there is no hope of her taking you back, then you have to find a way to move forward, but take the time you need to grieve as it is a loss.
I try to forget my ex and move on.  But every day I wake up and see several things she bought me and I feel like a sledghammer hit me in the chest and stomach.