Nasty cum

So my SO has always tasted good when i swallow his cum but i sucked his dick at like 6 this morning (4-29-18) and when he came it tasted disgusting. I don't know if its just from all the unhealthy food hes been eating lately or what but it was horrible and i didnt want to tell him cause i dont want him to get self conscious about it... I guess my question is what can cause it to taste bad?

UPDATE:

He has never eaten healthy though. I just found out he was cheating on me though so thats probably something.