Ending 1 - Take the dealer's drugs. Do Falcone's final mission.
Ending 2 - Spare the drug dealer, do Falcone's final mission.
Ending 3 - Take the dealer's drugs. Do not sell the drugs. Sell information at the bar, you should have 1500$ and drugs in your inventory. Go to the striper's house every chance you get.
Ending 4 - Take the dealer's drugs. Sell them to Falcone. Sell info at the bar. Get the info from stripper. Meet with the mistress.
Achievement without gun - Spare the dealer, visit falcone, go to strip club, news then dealer and enter trap