I'm a bit confused...
Your friend had a work visa because of her college degree? But had to leave after 6 months? I think she must not have been telling the story correctly. A college degree doesn't automatically qualify you for a work visa, and a work visa does not generally run out after 6 months. It continues as long as the job does.
What she is suggesting is, that after your six months are up you can go to Paris, have your passport stamped there, and then come immediately back to the UK for a further 6 months. Not only is this advice essentially irrelevant to your situation, as you are coming back to the US after 6 months, but, while it is not technically illegal, it is likely to get you red-flagged at immigration and sent back to the US anyway.
And never, ever, ever lie to Immigration. Tell them the truth (you can say your boyfriend is a "friend", as that's not really a lie): that you are staying with him for six months.