There is no form. You make the correct determination based on the IRS publications and the law, and then file your tax return accordingly. If the IRS audits your return you could be expected to show records verifying the amount of time you spend at your home in the U.S. and how much time you spend at your other home. Passport stamps, travel documents, etc. If you have been deducting anything relating to the property in Italy such as mortgage interest then you might reasonably expect to have a claim as a first time home buyer examined.
And my only goal is to help you get the information you need to make the correct determination, which is what you came here for, not to make assumptions on your behalf. If that is perceived as "competitive", sorry. I see a lot of blatently wrong information given to people. If I don't believe I can be of help, I remain silent. I hope I've been helpful.

