Demi Lovato is never one to hold back. The singer is referring to her former life coach, Mike Bayer, in her recent cryptic tweet, a source close to the situation exclusively tells Us Weekly. ?Good luck on your blog,? the 25-year-old tweeted in the early hours of Friday, July 6. The source tells Us that Lovato and Bayer, who worked together at CAST Recovery Centers in West Hollywood, had ?once been very, very close? and used to talk ?up to four or five times a day when they weren?t together working.?