Assuming nothing else happens before the ability resolves: You win.
After Bloodfire's ability resolves, the game sees three state-based actions that need to be performed.
- You should lose the game due to being at -3 life.
- Your Platinum Angel should be destroyed because it has lethal damage marked on it.
- Your opponent should lose the game due to being at -3 life.
The first of these is currently impossible because of the Platinum Angel, so the game skips that one and does the other two (simultaneously, Angel is destroyed and your opponent loses.) Normally, the game would do another round of state-based actions immediately after this in case there are more things it can do because of the change to the game state, and you would lose if this round of SBAs actually happened, but in this case the game is already over before that.
After Bloodfire's ability resolves, the game sees three state-based actions that need to be performed.
- You should lose the game due to being at -3 life.
- Your Platinum Angel should be destroyed because it has lethal damage marked on it.
- Your opponent should lose the game due to being at -3 life.
The first of these is currently impossible because of the Platinum Angel, so the game skips that one and does the other two (simultaneously, Angel is destroyed and your opponent loses.) Normally, the game would do another round of state-based actions immediately after this in case there are more things it can do because of the change to the game state, and you would lose if this round of SBAs actually happened, but in this case the game is already over before that.