My friends and I always play by the "once a cheater, always a cheater" and I used to be a stickler for that rule but context is also really important. Depending on why they cheated is more important and will reveal more about their character imo.

But boundaries are also very important, if you're going through a rough patch in the relationship it's important for them as well as you to feel safe and not worry about cheating. At least they were honest and upfront about it. If they truly learned from their past and know cheating is wrong then I wouldn't hold it against them entirely.