Literate fool! What do I say first? What a dilemma!! Let him marry her like Lennon said "love is the answer" and overlook everything else. Please convey my namaste/darshan to "bhabhi mai-would-be". It's great to have someone as bhauju with great familiarity regarding not only history but also geography. Just kidding. Hehehehe! Seriously dude, it will be pretty awkward I would say. But if it's okay with all three of you, go right ahead. But Never Let that "for old time sake" feeling creep into your head with your ex-gf-turned-sister-in-law. All the best. Buh-bye now.