Depends on the reason of the cheat... If it was because he/she have a sex drive that I couldn't satisfy, I think I can forgive. But if it's more emotional (he/she fell in love with the other person), then I'd just have a clean break.

Toxic is different and have many forms:
1) 1 side abuse the other side (verbally or physically)
2) Both side kept fighting and instead of motivate each other they demotivate each other

Relationship with cheating but not toxic:
1) Both side cheats but still stay together for various reasons.
2) 1 side cheat (normally guy side) but the other side do not mind (the one that's really ok with it).

These are just SOME examples, there may be more