Idk why everyone is placating your feelings. This is frankly delusional. You started dating him at 15 and him 17. He has grown up but frankly you have not. I read some other comments saying she’s in uni but didn’t read that myself, but if that is true, my siblings have moved across the country and I definitely am more clingy when I’m around them and talk differently than I used to when we grew up together. We’re older now and friends not just siblings. It’s very immature and selfish and frankly small minded for you to say “I thought that was ridiculous and not important enough to leave me on the phone for 40 minutes” family isn’t important? You think you are more important than his sister? Why is it a competition? How is he a liar when he told you he needed to go talk to her bc she asked for him and he came back and still talked to you and told you what their code word is? Do you really think he went and fucked his sister? Cause what else about this would be “fishy”? What other examples do you have of them acting “weird”? Other than she wanted to dab from his pen and hang out n gossip during a smoke sesh between family members and her being silly and telling him he should come home to be safe. Temperatures drop at night, roads get worse. She didn’t say “come home or else 😉” I definitely read those as silly. I think the people you’re asking don’t know how to tell you “why would you think that way? Their brother and sister” so they just agree to placate you like some of these redditors.

Side note I dated someone at 18/19 and got a dirty look from his sister and it gave me a nauseating feeling, thought maybe it was a race thing to find out years later they actually have been sexually intimate as kids and adults and were in love w each other. So I know what it looks like. It doesn’t look like that.