After more than 23 years in business, the Bear Brew Pub, a staple of downtown Orono and the preferred after-class hangout for a generation of University of Maine students, will close its doors at the end of May. A few weeks after that a new pub — The Common Loon Public House, owned by three Orono residents — is set to open in the same location in mid-June. The Bear Brew opened in 1995, after original owner Milos Blagojevic spent two years renovating a long-empty Main Street building into a cozy neighborhood brewpub.