re: I said no to marriage with my cousin - and getting emotional blackmail…
It’s a bit more than that.. What if he wants sex on the wedding night?
Apart from the ethical issues of deceit isn’t it likely the family won’t let her divorce him once they’ve married and have lived together as husband and wife - even short term..
(The OP mentioned her parents already told her ‘you’re old, who will marry you’.. imo they’d prob just turn round and say to her ‘who will marry a divorcee, you must stay with him’ and it will be threats and emotional blackmail all over again, possibly worse after all a broken marriage is far worse than a broken engagement)