I have seen a video on youtube a long time back, I don't know in which language was it. The story goes like this... A man falls in love with a girl, he's from the military the girl also loves him but they don't get married, the girl marries some other guy and after some time the male lead and the girl meets in a different city, she is in a kind abusive relationship and they start an affair but it gets out in front of her husband during some get-together or dinner they get into a fight and the guy leaves. After that, the girl decides to stop the affair and tells him that when he comes to meet her the guy gets upset and kills himself with a gun in front of her.

Does anyone know the name of the movie/drama? Please help me find it. Thank you.

Could it be Obsessed, kmovie from 2014? 

Some of the aspects reminds me of the synopsis of kdrama Road Number One, but As I have to watched it, so I don't really know if its the one you are looking for...

I am pretty sure this is not the drama you are looking for, but check out Taiwan drama A Touch of Green. it is one underrated and not much talked about drama with military, well specifically pilots and their wives/family during WW2 and the aftermath. Though the part of the affair is between a former pilot and the widow his senior officer. The widow is now fallen into hard times and is a mistress of a foreign soldier....