When you know, you know . This is, of course, what everyone says when they find the partner with whom they may want to share the rest of their lives. However, this sentiment very much applies to couples who are on the verge of falling apart. As a third party, you can often see the signs that two people are not meant to be. Sure, there are the obvious signs: fighting, infidelity, etc, but when it comes to the subtle red flags, that's when side remarks, body language, and social media posting bec…