Can extreme stress cause preterm labor?

I'm going through quite possibly one of the hardest times of my life. I'm 28 wks pregnant with #4, and I'm already high risk due to my age and history of preterm
Labor.
My son who will be 18 this year, informed us that he got the girl he had been dating past 3 months pregnant. She is 17 as well and emancipated and has no family besides an older brother who kicked her out when he found out she was pregnant.
My DH (sons step dad) kicked him out immediately after finding out. He had warned him multiple times the consequences of knocking a girl up.
He did however let him keep his truck so he can go to school/work.
He pretty much told me that either my son goes or he will leave. I'm 28wks , have no job at the time and can't start one due to my pregnancy. I have no way to support 4 kids plus a pregnant girl/baby on my own. So my hands are tied at this point.
My DH is causing so much more stress by forcing me to choose between my son/ him. He even made the comment that he seen this whole situation costing us our marriage. 
They did go live with my ex husband and his wife for the time being, so they are being taken care of.
But my heart is broken, I'm angry, I'm hurt... Just a mess. I can hardly get out of bed and function. I'm forcing myself to eat but because I know I have to support this pregnancy. But with try extreme amount of stress I'm under I just don't know what to do. He is my first and my only son. I love him without fail and would do anything to help him right now. I feel like he is going to hate me forever