Advice? Get rid of him
Actually you should have as soon as your sister told you he groped her
What hope there was for you and he then I dont know, but why are you stil with him?
How can you forgive a man who gropes, not just another woman, but your sister?
You have written doormat on your head for him ages ago, so he continues to wipe his feet on you. Do you truly believe your children are better off with him still there? They can still 'dote' on him if he lives some where else. He can be a better dad living else where IMO because he wont be contributing to these arguments
Watching porn doesn't make him a creep or a pervert BUT it makes YOU feel inferior, 2nd best and has whittled away and your confidence and self esteem and THAT is why he should stop
Put up or shut up but do not pretend everything is OK because he does as he is told for a few months at a time