help me solve this.

Hi My name is Robert, I have a problem that I must share as it is driving me loopy.

Last November I lost my job, ok got over it and went part time / semi retired, my wife took over paying the rent. In the new year we had to go bankrupt both of us, ok dealing with that, will be free September. In March my wife discovers a lump on her breast, and got it  sorted very quickly, she is about to start her second dose of chemo. I work 6-9 am, so I can nurse and look after her for the rest of the day ideal!  I have now discovered that my wife has been having a relationship with a work colleague for 2 years, she says that this guy just has a silly crush on her, but I have read her texts etc, and know that it is more than that. I don't want add to her worries due to this but she must make  a choice between me or him, I can not and will not be shared. After everything we have been through, this is just too much for me to keep inside me. Any advice ?