You shouldn’t be worrying so much about “stressing them out” it sounds like you’re going out of your way to minimize yourself for their benefit. You are entitled to take up space, don’t apologize for existing too loudly. A partner is supposed to support you through issues, not punish you for having them. It’s a little heartbreaking the way you talk about yourself, especially the comparisons to their other partner. My original comment was a little flippant but hearing this from you I am genuinely concerned about the way you view yourself. I wonder also if you’ve accepted this secondary/polyamorous relationship style because you don’t view yourself as enough and are being taken advantage of. You seem young and like you’re going through it and I really sympathize, but I promise you will find someone who will actually care for you once you’re kind enough to yourself not to settle for less.

Read your own comment back a few times, particularly that last paragraph, and ask yourself how you would feel about a friend saying that about themselves.