I agree, it sounds as if the see-though(I assume store-bought) divider is the problem here. Merlin is probably very stressed, seeing Peach all the time.
You can try to get some full, tall silk or live plants to line the divider on both sides to try and break up the line of sight a little more, though IME the fish just swim around the plants so thats not always effective....but its worth a shot.
Another option is replacing the see-through divider material with Craft Mesh, like in this tutorial: http://www.tropicalfishkeeping.com/d...ividers-21866/
I make all my dividers with this stuff, and I find that using two sheets and doubling up on the craft mesh not only makes the divider a little more stable, and secure, but my boys can't hardly see each other at all.