Anna,
Your best advice will come from your attorney........

Realtors can not give out legal advice, but I will say this:
I wouldnt have made the tennent move out until I had something in writing from you as a guarantee that you were going to purchase the property.
ANybody who makes any type of move without a contractual obligation is only placing themselves at risk.

I would think your lawyer's advice would be more qualified than any advice you could get on the internet. If you don't feel that way you should talk to a different lawyer. While technicaly you didn't sign anything, the seller did let the tenant go because of your implied desire to buy a house. Still, your lawyer is who you need to talk to as he'll know the situation (and all the state specific laws that may apply) better than anyone on trulia, besides, agents can't give legal advice :)