Just need to vent!!

Just want to start out by saying that I never in a million years ever thought this would happen to my sister she is the sweetest most compassionate caring person ever and she is went over and beyond for her husband but about 5 years ago she started having chronic pain It got so bad that she had to stop working and now she's on disability and my brother-in-law has been taking care of her ever since. .

So about two weekends ago me and my sister and brother-in-law got together for dinner I am recently divorced due to my husband cheating on me so me and my brother-in-law got into the conversation on how infidelity happens and his opinion it starts with a lack of communication and lack of knowledge he feels like you have to have something to talk about in order to keep a relationship alive which I totally get and understand. In the middle of us talking about this he says that is why I tried to be so knowledgeable about everything so I can keep my relationship alive and won't have infidelity issues . So fast forward to now my sister calls me up this morning in a panic, crying because she found text messages between him and his co-worker at work that was very inappropriate along with some pictures. The Audacity Of This Man to sit in my house and talk about infidelity but yet go out here and entertain another woman and while my sister is chronically ill is absolutely disgusting. .. I'm absolutely so sick and by it . I know she'll need someone to take care of her a lot and she can honestly come and live with me at any given time I don't know she's going to leave him or not but I know for one I would not put up with it I'm just fuming I just needed to vent!!