It's not possible to predict the outcome of any criminal trial without being privy to exactly the same information that your boyfriend's lawyer would have. Without seeing all of the discovery, conferring with the prosecutor and doing an independent investigation, I can only talk in terms of generalities.
The criminal history of the complainant and your boyfriend's lack of a criminal history are helpful to the defense. But the testimony of only one witness can yield enough evidence to convict a defendant if the jury believes him beyond a reasonable doubt and he may be very convincing on the stand. One simply never knows until he testifies.
The weaknesses that I see are: if the defendant knows your boyfriend from the neighborhood, he would be able to make an identification of him. What motive would he have to lie about your boyfriend pulling a gun on him? Also, if the complainant is a drug seller and your boyfriend's prints are in his house, even if others are too, this is still evidence that is not helpful to your boyfriend's case, because it's clear they know each other and that makes your boyfriend look less than perfectly clean despite his not having a record.
If your boyfriend's premises were searched and the police never recovered a gun, that would also be helpful fact for the defense. But if your boyfriend actually did commit this act, he would not be able to take the stand in his own defense, because no lawyer can allow his client to commit perjury and say he didn't commit the crime.
So while this isn't a bad case for your boyfriend, it is not a slam dunk for the defense by any means.