I'll go first.
1.) Titanic - If Jack lived.
2.) As Good as it Gets - Giant age difference and his ocd and his tendency to be really mean-spirited would eventually break through and wreck them.
3.) Moonstruck - Again giant age difference and Nicholas Cage is sort of a loon. Amazing chemistry but I feel they would hate each other in about 6 months
4.) Crazy Rich Asians - Will those horrible people she had to deal with for 5 days and made her utterly miserable suddenly change? Just because his mom is sort of ok with their marriage? Will her milquetoast hubby ever intervene?