One of my guinea pigs won't let the other one into their igloo?

At first I had 2 guinea pigs. Sebastian and Jack. Sebastian died of a URI. So I got Jack a new friend that is bigger than him named Bear. Jack is more outgoing than Bear. Bear is kinda a scardy-cat. Before they would both be in the igloo at the same time and it was no big deal. Now Bear won't let Jack into the igloo. If Jack trys to come in Bear'll push him out (not aggressively). So Jack will camp outside the door of the igloo. At first, I thought it was of his own choice but now Jack will go inside the igloo and Bear will make a rumbling noise and won't let him in. How can I fix this? Is it normal for that to happen?