This 50 year old man is spoiling my 18 year old girlfriend (Page 4)

I dont fancy discussing any of my personal issues on forum website like this, bcuz  at the end of the day, you wont get any answer. What you get is insults and attacks.
But, this issue is burning my heart day-in-day-out.

There is this gal of mine I thought of basing my life on. I deflowered when she was 18 years (2 years ago and I am 25 now). Ever since, we have agreed to nurture our relationship to marriage level. And, we have been trying to keep it.

Last month (Bad Sunday), I caught her red handed with my neighbor who is in his 5o’s Being Intimate with her when his family was away for church service (somebody that is as old as my father and is married with 3 children. One of his children is 18 years old as old as my gal).  I came back from church early and I saw her coming out of their apartment sweating and breathing heavily and with a strange odor coming out of her body (she came to my house when I was in the church, and I was not even expecting her that day. I was shocked to see her in my house without any notice). She was shocked when we met. I quickly sensed what has happened. I called her and she panicked and started rushing to the toilet, I followed her, grasp her hands drag her to my room. And I asked her, but it was too glaring cuz her tight was wet with Fluid dripping from her “blahblah”. (What annoyed me most was they didn’t use condom. Women are reckless; if she gets pregnant she will claim its mine).

She saw my eyes and confessed that the man tricked her (weeping seriously). She gave me a rooster and bull story that, he sent her to buy him a soap and when she came back to deliver the soap that the man descended on her and that she was afraid to shout because of shame and trouble it will cause between me and the man, she promised not to do it again and that she will be careful with him.

Last week, I went to her house to visit her mother, she was’nt at home,I waited for her for 5 hours. I left, when I could no longer wait. On my way home, just a stone throw from her house, I saw her coming out of this man's car joking and laughing with this man (I quickly sensed they are using Hotels or somewhere hidden)
I waited for her and confronted her, she just ignored me. On getting home I saw a text message on my phone telling me "never in my life should I call her again"

I made up my mind and forget about her (It wasnt easy but I did, cuz I had no choice).

Last friday my mother called that she came visiting her, that infact she washed her cloth and did all her Job and since then she has started begging again, still pleading and begging till this time on my facebook, SMS, email.

For the 50 years old man, I have a plan for him. I have toasted her daughter and she has agreed (We were both interested in each other before. In fact she expected me to make the move, but I didnt bcuz we are leaving in the same building, I feel its improper). But now, I will "f*****ck" hell out of her and impregnate her.
If she claims its mine I will reject it but I will admit Being Intimate with her, so that that useless man can feel it too.
But, regarding my gal, I am confused, do I take her back? She is just disgusting to me now…

Help me (I am angry and demoralized)