From my experience this wont be a problem. I am not Italian but I am from Europe and I got a visa without problems after spending a lot of time in the US previously (in one year I went there 5 times; for 3 months, 2 months, 1 week, 1 week, 1 week). Just prepare to show some ties to your home country in case they ask, show for example that you have a bank account, have family, and a degree (with transcripts). If things get really serious they will verify that you do not owe any money in taxes etc.
Bottom line, if you have nothing to hide there will be no problem. Just be honest in your interview, they wont consider it a big deal that you have an American girlfriend, they just dont want you to stay in the US and live/work illegally. By showing that you have a degree, some savings and a family you convince them that there is really no need for you to work in the US illegally.