The best answer to this is that we really simply do not know and almost surely never will know. Hitler was very guarded about his personal life so we do not know much about what really went on. However, people continue to speculate about this, largely because they tend to want to find some way to explain why Hitler was so evil.
Over the years, many people have argued that Hitler was gay. They have argued that the Nazis persecuted gays in part because of how much Hitler hated the fact that he was gay. However, there is no real concrete evidence that supports this theory. Most mainstream historians believe that Hitler was heterosexual and not particularly unusual in any sexual way.
While some people have argued that Hitler was gay, others have argued that he was sexually unconventional in some other way. People have claimed that he was completely asexual. Others have said that he was in some way abnormal in his genitalia. Still others claim that he was straight but had bizarre sexual fetishes.
Because sex is, for most people, a very private activity, and because Hitler guarded his private life more closely than many people do, we will probably never know for sure about his sexuality. However, people will most likely continue to speculate as we tend to want to find ways to explain why Hitler turned out the way he did.