A habitual offender is someone that has previously been convicted of a felony charge. The habitual criminal designation augments the punishment for second or subsequent felonies. In Michigan, anyone convicted of more than one felony can have his or her sentence lengthened if requested by the prosecutor and agreed to by the court.
Regarding the charge of Larceny in a Building (a 4 year felony): The elements of larceny in a building are (1) an actual or constructive taking of goods or property, (2) a carrying away or asportation, (3) the carrying away must be with a felonious intent, (4) the subject matter must be the goods or personal property of another, (5) the taking must be without the consent and against the will of the owner, and (6) the taking must be done within the confines of the building.
Under Michigan statute, your roommate can be charged with theft of your property from your home (even if the theft occurred in a common/shared area). Breaking and entering is not required for a charge of larceny in a building. Had they charged him with home invasion, my answer would be quite different [compare to breaking and entering with intent to commit larceny, MCL 750.110 (a 10 year felony) and entering, without breaking, to commit a felony or larceny, MCL 750.111 (a 5 year felony)].
Your desire to drop the criminal charges at this point is of little consequence. The decision to charge, or not to charge, is in the discretion of the prosecuting attorney. Once a complaint is made and charges are brought by the prosecuting official, it is not your decision to make.
That is not to say that there isn't anything you can do to lessen your boyfriend's exposure to incarceration and/or other criminal sanctions. The prosecuting attorney will seek your input/concurrence when discussing plea negotiations, and/or sentencing caps.
You should consider consulting with an attorney who practices criminal defense work but has experience working with victims in cases. There are things that you can do to help your boyfriend and an attorney may be able to help guide you through the process and make contact with the prosecutor on your behalf for the purpose of facilitating a resolution to the case that you and your boyfriend can live with.