Bf not staying hard during sex..

When your having sex with your SO has he ever had issues either staying hard or getting hard?? My bf and I were getting in the mood and during foreplay he was hard and all into it but then when it came down to actually doing it he couldn’t stay hard..we tried many times and it just wasn’t happening. We’ve been together 3.5 years and it’s never happened b4 just want to know if this is normal??