1) Talk to a lawyer.

2) If the seller accepted your offer in writing, and his
written acceptance does not say "time is of the essence," then
he probably can't legally back out of the sale. However, if
you really want the house, you will probably need to get a
lawyer to make clear to him the fact that he is not going to
be able to back out of selling to you.

3) Even if his acceptance *does* say "time is of the essence,"
then he probably can't back out of the offer if you can prove
that the delay was instigated by him, not by you. Talk to a
lawyer.

4) If you decide it isn't worth the hassle of forcing the
seller to sell to you, it will probably be easier to at least
make it clear to him that he should reimburse you for all of
your expenses related to the deal if he doesn't want to spend
a lot of time and money fighting with your lawyer. Again,
talking to a lawyer will be useful.

5) A legal dispute over the seller's right to sell to someone
else would certainly have the potential of changing other
people's minds about whether to sell the house. Therefore, in
many states, the sellers agent would be obligated to disclose
the existence of this dispute to anyone else interested in
purchasing the house. It might therefore be a good idea for
you to send a certified letter to the seller's agent, spelling
out the nature of your dispute, the fact that said dispute
would have to be disclosed to any other potential buyers of
the property, and the fact that failing to disclose said
dispute might leave the agent vulnerable to legal action
and/or sanctions. It is likely that this would have the
effect of accelerating the resolution of your dispute.
However, you may wish to consult with a lawyer about whether
this is a good idea and, if so, the best way to go about it.

6) Talk to a lawyer.

7) Talk to a lawyer.