Why does my one year old cry a lot when we're at my friends house?

My best friend has two twin boys and our sons have been having play dates since they were 5 months old but I stopped bringing him because I became more busy. Last week we went over and he cried each time I got away from him. He wanted to be held the whole time but he's usually not like that at home. I don't know what to do because we can't have a good time and he won't play with the boys. The boys have so many things to play with and he breaks my heart when he crys at my knees. He's probably just used to being on his own. How can I break him from that habit? Even when the maitnence guy came over to test our smoke alarm, he started crying.