Boyfriend didn't cum

My boyfriend and I have been together for two years and have had sex a lot but this past week we had sex and he didn't cum at all. normally after like 10 minutes he cums really fast but this time we had sex for like a half hour and he didn't cum at all I know it's crazy to think he's not attracted to me or had an off day but in the past two years this has never happened at all with him. Is something wrong?