Why else would his face smell like butt?

I suspect my live in boyfriend is cheating. We haven't had sex in 6 days. I've tried initiating and he has rejected all attempts. Yesterday was the first day that he finally let me at least cuddle with him. I noticed the butt smell right away. I was at work for 8 and a half hours. He only works when he can find gigs which is rare lately. He told me that he showered. Why else would his face reek of butt unless he cheated? He got mad, left and won't be back until Sunday evening, and is giving me the silent treatment. Is there anything else that would cause that repulsive smell?

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I'm now the breadwinner but the place is only in his name. I can't afford my own place. His $600 mortgage payment is a lot more affordable on my $14.50/hour income than an apartment that goes for $1400+/month in my area and we have 2 kids.
Why else would his face smell like butt?
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