Question need honest opinions

So I have received 2 text messages from 2 different people saying that my partner is cheating on me. I go away for study 3 days a week and I'm at work the other 4 days one week and 2 days the next week. 
I confronted him about it and he has said no he isn't cheating but has recently come home with a pimple like thing on his penis that made his penis red and swollen. We have been together for over 3 years and have never seen it before on him. If you were in this situation what would you think?

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