I worked at a day spa for nearly four years, and in all that time, we only had one complaint from a female customer about a male massage therapist, and even that was overblown. He forgot to adjust the table height at the start of his shift, so during her massage, he climbed up on the table at one point to reach part of her back, and she panicked.
You can't have love without trust and respect. Not only does she distrust you, but she doesn't even respect you enough to expect you to behave professionally as a trainer. Also, her insecurity about cheating might reflect poorly on her own behavior at work. Maybe she did something shady during one or more of her massages, so she expects the same from you. I think you should take the high road and pursue your new career, and let her do what she needs to do, which will probably be to break up with you. Let her be a hypocrite and deal with the consequences of her hypocrisy.
Good decisions come from experience. Experience comes from bad decisions.