According to the Diagnostic and Statistical Manual for Mental Health Disorders (DSM), exhibitionism involves exposing one’s genitals to a stranger and sometimes masturbating while exposing him or herself. In some cases, the exhibitionist is sexually aroused by the idea that the observer will become aroused. Exhibitionists are generally over the age of 18, male, and are intensely sexually aroused by exposing their genitals to unsuspecting strangers. In some cases they act upon the urges which ultimately leads to social and interpersonal difficulties.
In your case, it seems as though you may meet the criteria for exhibitionism, particularly because your fantasies or urges are causing relationship difficulties. Your relationship will likely suffer as a result of your behavior. You also risk losing the relationship.
I would recommend sex therapy. Sex therapists receive specialized training in issues related to sex and relationships. They specifically address concerns of sexual dysfunction, paraphilias and fetishes, sexual feelings and intimacy issues, and other related issues. Sex therapy tends to be short-term but length of treatment depends on the severity of the problem. Choose a therapist who is credentialed by the American Association of Sexuality Educators, Counselors and Therapists (AASECT) and who has a proven track record of success. This directory could assist you in locating a sex therapist in your community. Please take care.