Match Point is a must watch!

Man A fell in love with Woman B who is the sister of Man B.
Man B is engaged with Woman C.

Man A met Woman C, lust over her.

A few years later, Man A got married to Woman B. Man B broke up with Woman C.

Man A met Woman C, they had an affair. Woman B is trying hard to get pregnant, instead Man A made Woman C pregnant.

Man A got really confused with everything. He killed Woman C. He got away, because he's lucky.

There's more to it, I am just re-sorting out the plot, its more complicated than this and I think Woody Allen is a genius. So go and watch Match Point!