In the year 2018, there still seems to be some confusion when things come down to the difference between sex and gender. Sex is the biological sex indicated by someone's reproductive system whereas gender is determined through social role's of that individual. However, it seems that more and more each day people in our society like to debate whether there are two genders.
Let us preface this by stating your comments on "I believe that there are only two genders" is already incorrect. This is where an individual has begun to confuse the term sex with the idea of gender. There is a big difference between "male and female" versus "boy and girl." These are separate terms for separate identities. A baby can be born as a male or a female, determined by reproductive organs. However, as that baby grows and develops their identity and social roles, this same individual can identify as something other than their assigned sex at birth. This is in reference to their gender, this identity being completely up to that individual based on many different possibilities.
However, we are not here to discuss what makes an individual identify the way they do. We are here to discuss why your personal feelings towards that same person's identity does not, and will not ever matter. See, the thing is, is that it is not that individual, or any other trans* individual's job to make you understand the way they think, feel, and choose to live. Also, it is not that individual's job to make you feel comfortable with their choices. For example, if an individual in your life is in the process of transitioning, this meaning undergoing the process of changing their biologically assigned sex at birth, and they ask you to refer to them as their preferred pronouns, your only response to that request should be "of course".
No one cares how "weird" it is for you. No one cares how "hard" remembering their pronouns will be for you. Because the thing is, this process has absolutely nothing to do with you. Therefore, you do not get to have an opinion on what this transitioning process is like in any shape way or form.
Another example would be if you welcomed an individual in your life who has very recently identified themselves as non-binary. They approach you with the request that you refer to them with "they, them" pronouns. I have heard many different responses to situations such as these. Examples being things such as, "That's not grammatically correct" and "Well I knew (him/her) like that so I'm going to keep say that" and "That's really hard for me to remember so is it okay if I just stick to the old ones?".
The bottom line is that o one cares what your personal views and opinions on the matter of gender or sex. Because if you are not a trans* identifying member, you do not get to have such opinions. If someone in your life falls along this spectrum, be sure to respect their wishes and use the appropriate pronouns that THEY prefer you to use. If this is someone you genuinely care about, why wouldn't you want to let them know you respect them and their wishes?