@SwiggitySwoog I understand that approaching your sister about this situation is really hard because of how she might react, but you are not responsible for how she acts/feels okay? If you do go ahead with setting this boundary, I have a few suggestions to make when discussing things with your sister. Firstly, it's important to choose the right time and place that is a safe/quiet space, you could bring your boyfriend along too. Be as clear and direct as possible by expressing your feelings using "I" statements, and also you don't have to justify your feelings but rather explain that hand holding, for example, is more so seen as a sign of romantic affection and it's something you'd like to keep between you and your boyfriend. As for setting the boundary, be clear on what behaviour you are and are not okay with, such as "I would appreciate if you could avoid holding my boyfriend's hand in future". But also it is important to listen to your sister's perspective and how they feel about things, she might be upset by this situation, but that's why towards the end of the conversation you reiterate that you care about your sister and that you and your boyfriend are not trying to make her feel left out or excluded.
It seems like however you word/express things, your sister will react negatively, but again that is her own feelings/reaction, you are not responsible for these things. It will be a tough conversation, but I think it needs to be had.
I'm really sorry about this situation you are in, it's really challenging, but myself and everyone else on here has your back and we'll support you 💚
