AC1202, I experienced a number of different types of sexual assault and abuse throughout my lifetime, and it began in my childhood, and I've finally recovered from those experiences. I have developed some pretty significant insight and knowledge with regard to these types of situations, as well as human behavior and abuses.
When I type that it "doesn't sound right," I mean that a grown man of 19 absolutely knows better than to involve a prepubescent child in their lives, whether they are gay, straight, bi, trans, or whatever. This is a matter of morals, ethics, and boundaries, no matter what gender role we're discussing. It's just not kosher to "date" a child that much younger than one's self. That's a six year difference in age. To put that into its proper perspective, you have lived twice times 6 years, which means that he's slightly HALF of your current lifetime older than you are. It's just bad form and, in most States in the U.S., a criminal act. This is precisely why someone who is 15 years old is NOT considered a legal adult. They do not have the Life's Experiences to make INFORMED decisions, even though they are able to reproduce.
As a strict aside, how long has this man been your boyfriend?
Your description of him pressuring you also gives me pause for thought that he's deviant and may have offered you up to his friend as a toy. I'm NOT saying that's what he did, so please understand this. But, the scenario sounds all-too-familiar to me, and it is questionable, at the very least.
About your parents. There is the fantasy relationship, and there's the actual relationship. The two rarely cross paths, and this is simply a matter of fact, not a judgment. Your parents are either going to accept you as you are, or they aren't. Either way, you are not responsible for their issues. You cannot control anyone else's reactions, responses, feelings, attitudes, beliefs, or directions. The only person that you have any control over is your own self. This is why it's so vital to get that man charged with the crime that he committed, and get involved in some strong trauma counseling so that you can be the priceless and precious piece of this huge Universe that you are without feeling any sense of shame, guilt, or obligation to "fix" anyone else, save anyone else, or rescue anyone else. Tell them the facts about what happened. Talk about your feelings with them at a later date, because feelings may be associated with facts, but they are feelings. The facts cannot be disputed, but feelings can certainly be dismissed and devalued.
Sex is a very dicey thing, AC1201. It is one of the most powerful things that exists within humanity. It can be an indescribable part of a healthy, loving relationship, or it can be used as a weapon to punish someone to the depths of their soul. And, it can be used for everything, in between. But, at 13, there is no clear understanding of who we are, just yet. It is NOT unusual for children to have their first experiences with the same gender - it simply isn't because our friends are typically the same gender as we are, and our childhood friends are typically the people that we trust enough to begin exploring with. Sadly, because we don't speak openly and frankly about this sensitive subject, we assign labels at a point in a child's lifetime when they don't even know who they are, yet.
SO........try not to worry about whether or not you're gay, bi, or whatever. JUST concentrate on recovering from the crime that was committed against you and developing into an emotionally, physically, and spiritually (NOT religious) healthy individual. Loving yourself, FIRST, is the most valuable thing you can do for yourself, today. Everything else will fall into place it due time.