Dear J,
This dream is very symbolic of the break up in your relationship. A dream with your boyfriend in it (or an ex-boyfriend in this case), particularly one who is dead in the dream, symbolises that something within yourself is no longer functional, or in other words dead. Often after splitting with a boyfriend you can feel dead inside so this makes perfect sense. The dream is also, not so gently, telling you that it is time to let go of the relationship.
The fire in the house says you are needing to undergo a transformation. It can also symbolise destruction, desire, transformation or anger. I would suggest that it is a combination of the above; destruction of what you shared with your boyfriend (the house representing your relationship), desire to have what you had back again, transformation of your relationship and anger over the split and him backing out of buying the house.
You are searching for everyone in the house, which is symbolic of missing something or needing something in your life, in this case you are missing your boyfriend. You may also be searching for a solution to a problem. No one hearing you in the house as you call out to warn them about the fire suggests that you feel as though you are not being heard by those significant to you in your life. Your subsequent finding of your boyfriend indicates you are identifying new facets of the relationship, which suggests you are slowing coming to terms with the splitting up of the relationship.
Waking up feeling empty and upset makes perfect sense as you were physically seeing and feeling the effect of the loss of your boyfriend.
Love
Cassandra