Why does he cum sooner than before?

I'm clueless about this and genuinely would like to know.. is there a specific reason or reasons why a man may cum sooner than he used to in the past? Backstory, been together for about 2 years, always go at it for long periods of time, different positions, etc because he took awhile to cum and had a high sex drive... Now we went a few days without it, and when we did he came rather quickly as opposed to his usual? Stress, illness? It just didn't seem his normal.