You can write to the USCIS and tell them you believe she has committed fraud and married you just for the green card but you will have a difficult time proving that.
The problem I see is that you are not living in the US or Saipan but took a job in Saudi where she could not go or she could loose her status.
So since you are not living in the US or Saipan, she cannot live with you so it is not unreasonable for her to travel and live in the US mainland while you have left her and Saipan to work in Saudi.
USCIS will not see her as abandoning you because as you say you travel a lot for your work and were absent from her often while she lived in Saipan and then you accepted work in Saudi. She traveled to the Mainland because you were not living with her or were intending to take work in Saudi.
I don't think USCIS will consider her move to the US mainland as abandonment because you traveled for work as you say "alot" and were applying for work in Saudi. They will say you left her because you left the US territory to work in Saudi so she is not doing anything wrong going to the mainland. You are not in Saipan to live with her. I don't think the USCIS will say she had to stay in Saipan while you were constantly traveling and then applying for work in Saudi and were leaving Saipan and were not living with her.
You can try to claim fraud but you will need some solid evidence where she wrote you an email or text and said she only married you for the green card. Otherwise, it appears like a natural breakdown of a marriage because of your absence from Saipan on frequent business trips and seeking work in Saudi. There is no obligation for her to remain in Saipan if you are not living and working there.
I know this is not what you want to hear but she has not left you. You took work outside the US while she has remained living here.
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