This is completely your decision. If you are not comfortable disclosing your sexuality to your Aliyah advisor, you don’t need to.
However, your adviser’s role is to provide you with information and advice on where to live, how to find work and to help you find your community, so the more you are willing to share with them, the better their better advice will be.
Please note that there is no institutionalized homophobia at Nefesh B’Nefesh or the Jewish Agency and you will be treated with respect whether or not you choose to disclose.