Lady Gaga's "user" boyfriend says he's sitting on millions of dollars worth of sex tapes

It's hard to imagine Lady Gaga with a boyfriend, in fact there are almost no photos of 30-year-old Luc Carl in Gaga's presence, but apparently the fellow muso has got a pretty strong grip on her. And according to some worried friends, he's just using her to boost his own career.

“Luc leveraged her fame to get a book deal,” a source tells In Touch magazine.

Gaga has been dutifully promoting the book, The Drunk Diet: How I Lost 40 Pounds… Drunk. A Memoir By Luc Carl, while promoting her own new single 'Born This Way'.

“I am on the drunk diet,” she told reporters recently, claiming she owes her trim body to her boyfriend's unorthodox regime of drinking to excess every night.

But friends say Gaga suspects that she's being taken for a ride, she just doesn't have the confidence to do anything about it.

“Deep down, she feels that Luc is only back with her because of her fame and wealth - he didn’t want her before she became famous,” a friend tells In Touch.

“Luc is borderline verbally abusive to Gaga. He has jokingly threatened that she best not cross him because he could smear her name,” adds the source.

Apparently Luc often brags to friends that he's stockpiling millions of dollars worth of graphic sex tapes starring himself and Gaga.

Adds the source, “Because of her very low self-esteem, Gaga believes Luc is the best she’ll ever get.”