Didn't watch the whole game, but from what I saw West Brom deserved the 3 points. Definitely wasn't a penalty at the end, not sure about calling it a dive but he definitely went down pretty easily, although then again players go down in a similar fashion all the time, particularly in a situation such as this one tbf. Either way Mariner bottled it.
Although that's football. You're lucky as **** one week then the next you get ****ed over. Swings and roundabouts.