How long should I let this go on for?

My boyfriend and I talk on skype and its the only way we talk to each other. Twice today and 1 time last night he saws brb then 30 min later he gets offline then he doesnt come back on. I really like him and I want to tell him that its bothering me but right when I am about to say it he says brb. I dont like it when he does it. What should I do?