Struggling with slowing down my horse's lope?

Alright, well I've been riding a 15 hh gelding for the past year, and everything has been fine, but he loves to run. And when we lope, its like he's goes faster and faster everytime. I'm not sure what to do, and he just keeps speeding up more and more, and it just keeps getting worse and worse. I'm actually starting to lose my confidence with loping, and actually dislike loping him because he goes so fast, and I don't know how to slow him down without breaking him down into a trot. Please, any advice, tips anything please?