To clarify:
Your husband's immigration path is in his hands. If he chooses to stay, he can simply file an I-751 with a divorce waiver (if he is currently has a 2 year Green card) However, it is essential, imo, that you obtain a good divorce attorney to protect yourself physically and financially. As stated, an I-864 and your obligation remains in force until the immigrant:
1. Becomes a US citizen: or
2. Leaves the US and loses status as a Green card holder; or
3. Accrues 40 quarters of work credit; or
4. Dies
A divorce neither relieves you of the I-864 obligation nor requires the immigrant to leave the US. Good luck.