Need advice

Ladies I know it's a silly thing to worry about, but would you be mad if your SO has a 30 day streak on Snapchat with a different girl? We live together and I don't think he's cheating but I've been getting frustrated by them talking and hanging out. She just had a 21st birthday and he went over and ended up staying the night. She lives with her BF and a lot of people were there but it still bothers me. She is kinda slutty and acts like that with a lot of guys but I think she should be respectful of our relationship when she knows it bothers me. She will ask him to go shopping with her and he will hold her bags which bothers me because he won't with me unless I ask him. I am kinda just so frustrated and done arguing about it and I don't know what to do. Any advice would be helpful.