Blog reader wants to share heartbreaking experience he had two days ago

Matured and constructive comments only, please.

Hello Laila, for the dignity of the people involved, I plead you hide my identity. Not just for their dignity I must confess, but sincerely I'm hoping that some of your readers will give me the advice/support I'm really praying to get (which I will reveal at the end). 

This is my story. 

I have been dating this girl for about 6 years now. I was really hoping to propose to her this year once I'm through with my present contract. This contract was really a life changer for me.  

Mary (not her real name) has really been through thick and thin with me (nne, I have suffered in this life). You know that kind of suffering that you wake up in the morning and you are not even sure of what you two would have for breakfast not to talk of dinner. Well, she was always there for me until I had this present contract. A contract I now doubt her involvement. 

Sometime in January, we met this guy she went to school with. (His name is Joe, that's all she told me). After the normal catch up that involved Mary telling him how we have been trying to make ends meet, he gave me his card and asked me to see him the next day. 

I was in his office the next day as agreed and he told me he wanted to use me and execute a contract he couldn't execute himself since he worked with the company. That at the end, the profit will be shared 50/50. I agreed considering the amount involved. 

This was actually why I thought I got that job, strictly because he felt he could trust me at least coming from Mary. 

Laila, my story long but to shorten it, two days ago, I walked into Mary and Joe making out in my own house. She thought I had traveled because I was supposed to go to Onitsha to buy some materials for the job.  

I love Mary, I no go lie. But I've not been myself these past two days.  

• Do I forgive her, finish the job and get married to her?
• Or do I bail with the 30% mobilization fee which is far more than enough for me to leave this life with her and disappear? This will mean Joe hanging for it since he recommended me.

I'm reading and waiting for advice. Please help me.