The backside has died from lack of light. Prune the dead parts off and move closer to the glass.

I'm going to sound rather negative but imo you might as well ditch this plant. Most evergreen, vining house plants hail from warm climates. They can cope with the heat and dry atmosphere inside a home. English Ivy is native to temperate climates and thrives in a cool moist atmosphere. It just doesn't make a very good house plant. It is particularly prone to spider mites. Personally I'd swap it for an easier subject like a Cissus or Epripremnum. That said you could try putting yours outside in the shade for the summer. Unless you live in a hot dry climate.

p.s. you'll probably find you have more than one plant in the pot. Growers put several cuttings in a single container. One might be in trouble and the others not.

Canary Island/Algerian Ivy is better in the house. Never grew English Ivy here inside, and outside it is a WEED!