Larceny by scam/larceny by trick, is simply another form of theft
that is committed by fraud.
Yes, plenty of people get charged for crimes and don't have co-defendants. Sometimes, even when two people are together, only one will get arrested. It all has to do with the facts and circumstances of each case.
A State Attorney is free to prosecute a case the way he sees fit. But you have this the other way around. The lower the level of larceny, the more serious the crime. A Larceny in the 3rd degree in Connecticut is a Class D Felony. (See link)
A larceny in the 4trh Degree is a Class A Misdemeanor
. (see link)
The difference involves the value of the property that was allegedly stolen.
A state attorney can absolutely reduce the misdemeanor (or the felony) to something lower for purposes of a dispositon, if the defendant wants a deal and the prosecutor is so inclined. On a first arrest, he can even agree to a diversion or deferral offer, which is a special form of supervision where after taking anti theft classes, paying fines, and doing some community service, someone who completes the requirements successfully can get his or her case dismissed at the end of their supervisory period, so that they won't have a criminal
conviction on their record.
Regardless, if your boyfriend is incarcerated, he should be able to get an attorney appointed with him with whom he can fight his case if he wishes to go to trial
and put the State to its proof of if he would rather have a deal negotiated for him.
The best thing you can do for him at this time, since he'll have a lawyer, is to help raise the money to bail him out. If he wants an offer he'll get a better one once he's out on the street because while he's "in" the State Attorney is holding all of the bargaining chips.
Good luck with his case.