Boyfriend is flaccid

My boyfriend of 4 years and I always have a great sex life. Always been amazing. 
However we've tried to have sex the last 2 days and he was hard at the beginning and just went flaccid after like 5 minutes. He didn't get hard again and didn't cum once. 
Is this my fault? What can I do? We didn't do anything different to normal. 
Edit: He was flaccid after like an 8 minute blow job.