Thank you all very much.

No, the marriage (while rocky) would not have ended in divorce. They were both committed to the situation, for good or bad.

My BIL had a history of cheating on my sister. It tore her apart. I feel sure that his behavior contributed to her early death.

Thank you for validating my feelings about him seeing another woman so quickly after my sister's death. I really wasn't sure how to feel, but now I believe the 'red flag' in my mind and heart is there for a reason.

I am angry because he is traveling around with this new woman...my sister begged him to travel with her; he never would. My sis predicted that he would meet another woman and do fun stuff with that woman within months after my sister's passing, and she was spot on