This all started about a couple of weeks ago my boyfriend got what looked like a pimple on the side of his neck. As days went by the "pimple" got a lot of puss inside so I convinced him to let me squeeze it. A lot of puss came out and the bump went down. Little by little the bump has returned and again is full of puss and bigger then before.
He is now worried and is under the impression that it is not a pimple infected... what could this be.

It could be that you didn't get all of the infection out, and it continued to spread. If I were you, I'd go to a doctor, and see if he/she can lance it, or give him some antibiotics. Do not attempt to squeeze anything! It can cause troubles just like what's going on. Never squeeze a pimple or a boil. If you cannot afford a doctor, try going to one of those "minute clinics" that are springing up in drugstores and such. Or a walk in clinic. They can help you.