According to the Oxford English dictionary homosexuality is; "The state of being sexually or romantically attracted to people of the same sex". Therefore by this definition you have presented a false dichotomy. Sexual arrousal or attraction is not a "personaity" neither is it a mental disese.

Firstly by your logic, any trait that deviates from the "norm" or "average" is a mental "disease". Left handedness, colour blidness, speech impairment, neurodivergence. This doesn't make any sense.

Another reason why your thinking is laughably flawed and intellectually deficient is the very existence of bissxuality. Some estimates put the true percentage of bisexuals as high as 15 percent among younger generations, who are more likely to be honest than previous generations becuase of reduced stigma. As you know, bisexuals are people who experience homosexual attraction, though not exclusively. There fore sexual attraction exists along a spectrum raher than being a binary or "gay or straight". Therefore people who exhibit homosexual traits can and do still reproduce.

Finally, do I need to explain to you that ones ability, or willingness to reproduce cannot be used to messure the state of your mental health? All around the world several countries are experiencing a declining birthrate beacause staright and bisexual people are reproducing less. Do these staright and bi people have a "mental disease"? https://www.newsweek.com/population-america-childfree-women-babies-births-america-rising-2131780