I think your instincts are spot on. It's easy enough to be all sugar and spice when things are going well - the real personality shows itself when things are difficult. This Jekyll and Hyde thing is a bad sign. Don't go into a doubtful marriage because you are afraid of hurting his feelings. Your future, your life and happiness are at stake. The following links might be helpful:
Ultimate Self (realizing personal potential) | Abuse
Ultimate Self (realizing personal potential) | Relationship stress
Ultimate Self (realizing personal potential) | Identifying Mr or Ms Wrong