So, she thinks I'm cheating on her (I'm not)

[OneFootInTheGrave]

If she is in denial about your illness, for sure this is the cause of such weird behaviour. Ultimately you will need to sit down and talk, disucss what would be good for both of you and the kids given the situation and try to make best of it.

Some sort of "facing the truth" discussion (which is unfortunately one of those few cases that are worse than if you were cheating), should be on the table.

[kentonio]

For years I've let her vent first, say all kinds of things, and then after she calmed down, told that I will not tolerate this kind of behaviour.

Perhaps you're long overdue a bit of a blow up of your own. Over time people can come to mistake reasonableness for weakness.