Yes, but sponsored immigrants have successfully sued the sponsor using I-864 as a basis for support (basically the difference between immigrant's salary and 125% of the poverty level - the three that spring immediately to mind are Stump, Cheshire and Moody).
If immigrant is working, OP probably wouldn't be on the hook for much support (if any). But - and this is a worst case scenario - if he knows he can file suit, and refuses to work, and then actually goes ahead and files.... OP could be on the hook for providing 125% of the poverty level until the immigrant naturalizes, dies, earns enough qualifying quarters or leaves the country permanently. Unfortunately the courts have indicated that the sponsored immigrant is under no obligation to work or even seek work (and trust me that peeves me to the Nth degree!).
Granted the few cases that I've found are the exception rather than the norm, but I wouldn't be surprised if more and more divorced immigrants try this route to obtain spousal support where none would ordinarily be awarded.
Now I need to back up a second
Your husband doesn't need a further sponsor because your sponsorship is pretty much a done deal; even if you divorce he would probably be able to obtain his 10 year green-card provided that your marriage was legitimate.
Also the contract is technically between you and the government and because he is a third party he probably would not have any standing to change or waive that agreement, though it certainly wouldn't hurt if you could come to some arrangement.
You really need to speak to a lawyer - and one who can help you with the immigration stuff.

