Relationships are irrelevant. Interstate private transfers are prohibited by the federal GCA.
As a non-licensed Massachusetts resident, you are unable to acquire a long gun from a dealer out of state, since you are unable to acquire a long gun under the laws of your home state, and such transfer (long gun from FFL to in-person out of state resident) are required to be in compliance with the laws of both (1) the state where the transfer is occurring and (2) the laws of the transferee's state of residence. (People have been subjected to federal prosecution and been convicted for such violations in the past)
Even though Boston makes it relatively difficult to get an LTC-A without restriction, you should be able to get an FID or LTC-A (with restrictions) except for some extra delays and steps (e.g. the Moon Island qualification for LTC applicants/ renewals). Either of those (an FID or restricted LTC) would be sufficient to allow you to lawfully acquire a long gun (an FID will limit you to rifles and shotguns which are not "large capacity weapons") and maintain it in your home and transport it to a target range. That would meet your stated desires and you would have the convenience of being able to have the rifle/shotgun at home where you can take more steps to ensure that it is secure.
Ok understood and thanks for the clarification. I don't want to apply in Boston because in the next year or two we are definitely moving, so if I stay in Massachusetts I do not want to be locked into 6 years of a restricted license, which as absolute guarantee for me living in Boston. I know many instances of individuals being locked into their restricted license because often Boston refuses to prematurely expire said license (so the individual can re-apply in green town). I would rather wait it out as much as that kind of sucks.