There is no research showing any definitive connection between memories of past heterosexual abuse and future homosexual orientation development. What we use to see in clinical practice very often is people who were victims of sexual abuse by people of the same gender, to develop conflicts around sexual orientation and identity, sometimes developing homosexual ideation - behaviors, which could become very conflicting due to religious and social beliefs - standards, morals and specially because of the prejudices and discrimination arising from them.
Psychotherapy could be used to attempt to change sexual orientation but it is not considered an ethical - acceptable practice to consider any particular sexual orientation as abnormal or as mental disorders at all, as it is unethical to use therapy to push a specific sexual orientation in conflict with the client's real sexual identity and orientation. Psychotherapy should focus on supporting the person to explore and better understand himself, vent and process feelings related to any issues or challenges affecting - undermining mood, functioning, relationships and any life area, promoting improvement of coping skills, sense of self-worthiness and resilience. It should always point at eradicating prejudices and stereotypes damaging the person's mental health and well-being, empowering him to be himself, to feel fine with himself and to shape his life in consistency with his uniqueness; developing and open, non-rigid mind, promoting further learning and growth, embracing his whole self, especially any challenging or conflicting experiences requiring personal work.
The psychotherapist should be a unique "therapeutic" facilitator and supporter, adjusting his competence-experience to each client's uniqueness, for their support to be ethical and effective; again, always promoting health and well-being, respecting the client's values and belief system, but challenging any inconsistency or dysfunctional belief-behavior leading to undermine the person's health and well-being.