You are certainly taking a chance with custody of your children if you marry a sex offender. The children's father would definitely have an argument of change in circumstances to change custody from you to him. If there is not father in the picture, CPS might be interested in the situation.
The law dictates that the "best interests of the children" dictates everything with regard to children, custody, etc. Do you think it is in the best interest of your children that they be in a household, raised by a sex offender? Especially a sex offender who cannot follow the conditions of his probation?
That said, "sex offender" is a term that is far too widely applied, in my opinion. A sex offender can be a young man, say age 19, who has a relationship & obviously sex with a girl who is 16 - as long as she is at least 1 day more than 3 years younger than him. Since your fiance did get probation, this suggests to me that his offense was not heinous - that perhaps he is not really a threat.
What might happen with your children depends in great deal on who is complaining, and then, on what an investigation into what your fiance actually did, turns up. If he is a true rapist or a pedophile who prays on young children, then you can easily guess what may happen.
You have to ask yourself what is best for your children. They come first. Or, you can give up your kids and put yourself first.
Although I have answered the question to try to help you, you should consult with a lawyer in your area in person on the matter. In addition, my answer does not establish an attorney-client relationship between us.
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