My Girlfriend Is Having Séx With Men In Bank To Get Promotion

Trouble started in my relationship with Amara early last year when
she started going about with one fat lady in our area. Although we
live in the same house, after I went to see her mum and also took her
to my family in Delta State, but I hardly touch her at night, unless I
struggle before she will allow me do anything.
Since she started following the fat lady, she changed her name to
Amyy and I was told it was the lady who got a job for her in the
bank. As soon as she started the work, my girlfriend changed totally
as she dress very badly and when I complain she said I should get her
a job if am man enough. NASTYGIST can you imagine?
In just 8 months of working, the bank have promoted her and she now
wears costly gold and perfumes.
I can even say that am ashamed to say this, but Amara brought
another man to my house three weeks ago when I went to work and a
boy in my compound used his phone to capture them making love...
It was last weekend that I didn't go to work that this boy decided to
show me the video. It was like blue film and I wonder how many
people would have seen my girlfriend getting screwed in his phone
before he came to me with the video. I feel like crying.
I confronted her and she denied. She said it is computer manipulation
that I should not believe all this boys that know how to operate
computer. In fact Amara is taking me for a fool but I don't know how
to tell my mum that I'm not interested again and chase her out of my
house.
I'm 36 and my mum once said any mistake this girl make I should
forgive and marry her. What can I do?