What Is It You Are Not Telling Me?!

My husbands brother and his wife are having some sort of marital trouble. I know the finances are a BIG part of it since she was raised in a wealthy family and because she got married and had a child young the refuse to pay for anything but she has not cut back on her spending. Another big part of it was that he was in the Army and out of the country a large part of the first few years they were married and now that he is out dynamics are different. Now she seems to be avoiding me and whenever we have a date to get together so the cousins can play she bails on me and says she is sick. The last few family get togethers she has skipped also and she has been making frequent trips to the OB/GYN. She swears she is not pregnant and says she has a cyst but that is not the problem and they are doing "tests". They have been running tests for over a month now and she still won't tell me whats going on. Now my husbands brother has talked to him about everything but my husband is so damn honorable the refuses to tell me anything since he promised his brother he wouldn't. All he will say is they are going through hard times and not to jump to any conclusions or ask any questions. I asked him if she had an STD and he rolled over and said he was NOT talking about it and went to sleep. So if she does have and STD is she fooling around or is he fooling around and brought it home to her? I know it is none of my business but I really want to know!!