The reason they insist upon this is their teaching that their organisation is the one true church, and that they are the only true Christians. Not only do they despise Trinitarian churches, but they also despise other non-Trinitarian sects such as the Christadelphians.
Now most religions advise marrying only within their own religion, and that does make some sense. If religion is fundamental and important in your life then it's difficult to be in a marriage with someone who doesn't share your beliefs. But Jehovah's Witnesses make this an order, not advice, and because they say they are the only Christians then it follows (according to their logic) that J.W.s only marry other J.W.s.
Now since one of their teachings is that they are the one true church (which other religious movement makes that claim?) then when you see corruption in their organisation then you need to question not only their organisation but their whole theology.
As you are disillusioned with them you should stop attending. Unfortunately this will mean they will all be commanded to disfellowship you, including your whole family if they are J.W.s. So this will be a huge change in your life.
You still seem to believe in God, but now that you don't believe them to be the one true church you should question many of their other teachings. The New World Translation, for instance, was commissioned by the Governing Body whom you recognise to be corrupt. Their teaching about blood transfusion was decided in the 1940's and has changed with time; if you're ever in a medical emergency you should take the advice of the treating doctor, not the J.W.s.
Maybe you should attend other churches and see how they interpret the Bible. If you aren't convinced by them, you will at least see that the J.W. interpretation isn't the only possible interpretation.
You don't need to marry or choose a life partner at this time. Whilst you might want to have a relationship with a man, you are re-thinking your whole belief system, and therefore it's better to make a choice after you have thought about this. Be careful if you are dating "worldly men" as most believe that sex before marriage is perfectly OK, but if they talk you into this then you should use contraception.