The bottom line is, the seller will be forced to clean up the oil mess,no matter how bad it is. The bad thing is, this will take up some time and you will need to be patient.
This is a lawyer question. there are ways out if they drill and the water table has oil you should have an out again if the lawyer and the agent are not staying in contact with him i would say find a new agent if you step-away from this deal . Again i say follow -up with the lawyer and ask what is your outs ..
Century 21 Gemini LLC
Have your boyfriend look over his "Contract and Addendum".
Resolve, I am certain your boyfriend have a list of "Contingencies" that would protect his interest.
Note: Emotion have nothing to do with law.
But I'm going to make a point that you can check with your Attorney;
It would appear that the Sellers have been acting in good faith and you have taken steps to work with them; I would think that you might lose and Arbitration/Mediation over the Deposit at this point.
But, question; if you've gone this far, why not see it through?
Unwavering Commitment to Service
If you really like the home, you may want to stick with it. I know how frustrating it can be dealing with home inspection issues, but it will be worth it in the long run if you can get the home you want at a good price and know it is safe.