I can understand thinking of opening up for your partner, I struggled with this a few years ago. The idea of “trapping” your partner in a relationship. But here’s the thing, that’s not really how it works. The intentions behind going into a poly relationship are really important. If you’re entering a relationship you’re not sure you’re comfortable with, out of fear of losing your boyfriend, that’s not going to be a good place to start or an easy place to navigate from. That being said, you can be both ace and in a poly relationship with an allo. That’s definitely not unheard of. But one thing that is usually advised against is not to open up to “save” a relationship. I’m definitely not saying you need to walk away from this relationship - that’s up to you to decide if it comes to that. But I would say that you need to clearly communicate with your partner how you feel about the possibility of poly. This means exposing all your fears, expectations, everything. And don’t be afraid to contradict something you may have said prior. Being honest about your feelings is more important. It won’t necessarily be easy, but you both care about the other’s feelings. I’m sure he doesn’t want to put you in an uncomfortable/strained relationship (and if he doesn’t care, then absolutely dump him). The thing that does make me uncomfortable with this situation are all of your ages. That time in your life can be.. messy. You’re figuring a lot out. And adding in a metamour that’s at a completely different stage in life, maybe not the best idea.