Help Me Ladies!!!

Madison
Ok ladies I need your help! I've never been a jealous person in any of my relationships but I'm having some issues with my boyfriend and his sister. They've always been extremely close which has bothered me at times because he chooses her opinion over mine and feels very committed to her in ways that include dropping everything to help her out with anything she needs. I LOVE his sister. She's great, sweet and adorable. I have no issues with her at all. However, I read a text message (I was not going through my boyfriends phone, it was literally left open on this text) that said: "Good morning pal! Just wanted to say good morning and I love you. You mean the world to me! Xoxo" from her. Is this a normal brother-sister text message or am I right to feel a little uncomfortable? Also - should I ever say anything about feeling uncomfortable with their relationship or do I keep this one to myself?
Thanks!