Hello vampykisses: I'm sorry you are in this most difficult situation.

I do think this development is something you & your fiancé need to talk through, if he is willing, either just the two of you or with the help of a marriage & family counselor. Of course, therein lies the problem.

From what you wrote, it sounds as though your fiancé may not be willing to talk about it.

If not, then you are simply going to have to decide whether or not this is a situation you can live with. As others who have replied to your post have said, you have many years ahead of you. And you are the only person you can control.
In answer to your title question, no I don't think this has anything to do with you. Your fiancé has something going on of which you are only now becoming aware. In general, this is not all that unusual I don't believe. You don't mention, in your post, if your fiancé's interest is in trans men (ftm) or trans women (mtf), or both. I'm going to assume his predilection is for trans women (mtf). Assuming that is the case, there are a couple of different possibilities here. Your fiancé could be interested in trans women sexually. Or he could, himself, be hiding a transgender secret.

Either way, of course, if he won't talk about it, then there's no way to resolve the problem, if in fact it can be resolved.

You mentioned you have no family you're close to & not many friends. So perhaps there's really no one , in real life, you feel you can talk about this with. If that is the case, you may want to consider seeking some individual counseling / therapy services for yourself so that you have someone with whom you can talk all of this through. Simply allowing it to keep ruminating through your thoughts is, in my opinion, only likely to make the whole situation seem all that much more confusing.

We here on PC can be supportive. And I hope you do continue posting. But what we can provide is not a substitute for real life help.
I see this is your first post here on PC. So... welcome to PsychCentral… from the Skeezyks!

I hope you find the time you spend here to be of benefit.

PsychCentral is a great place to get information as well as support for mental health issues. There are many knowledgeable & caring members here. The more you post, & reply to other members’ posts, the more a part of the community you will become.

Plus there are social groups you can join & chat rooms where you’ll be able to connect with other PC members in real time (once your first 5 posts have been reviewed & approved.) Lots of great stuff! So please keep posting!