Girly-  I am so sorry you are here.  This is a horrible experience to have to go through because it rightfully causes one to question what had been unquestioned - your heterosexual connection with your fiancee.

In this case, there are multiple red flags that are flapping furiously in your face right before you commit to spending a lifetime in this match.

Mainly, the fact that you found out about his sexuality, his cheating, and the fact that his behavior might have health consequences for you - all at once because you discovered evidence he left behind.

This is too much of a bombshell for you to just go ahead and marry him as though this isn’t happening.

It is happening.

If anything, spend some time really reading about other people’s experiences learning they are in mixed-orientation-relationships AFTER THE FACT.  Spend some time really thinking through your situation.  Talk to a therapist. 

The fact that you found out BEFORE the wedding is the biggest blessing in disguise.

Good luck!