Visa Requries leaving 90's (Singapore)

Hi Everyone
I'm moving from the United States to Singapore in December with boyfriend. He has a work Visa and I do not. His assignment is for three years.

I've heard that I will need to leave every 90 day's. Has anyone ran into issues of them not allowing one back in after 90 days? How long will they allow me to keep reentering.

Thanks much in advance for any information.