Husband

My husband texted me this afternoon to say that he is going to the gym with his sister after work. I haven't seen him all day, but whatever, right?  Health is important. Just saw her snapchat story that she went running at 6:00. He gets off at midnight. I asked him if she was going back, because I saw that she went earlier. He just said "yes, love you."  This is suspicious to me. He has never given me a reason to not trust him, but isn't that how it always happens? You don't have a reason to not trust someone and then all of a sudden, you do?