When does it get better?

It has been almost 2 months since I witnessed my BF in bed with his other woman. I was starting to feel better, not think about it so much and actually have peace about it.  Last night I was heading to bed, happy, and all of a sudden my mind started over thinking again.  I ended up crying myself to sleep and could not stop dreaming of that day.  I slept only a few hours, was late to work and just can't stop thinking.  I am very busy but this mind of mine won't let me function.  When does it get better and these horrible moments go away? I just feel like life is not worth it.  I pray to God to let me leave this world.