There is something terribly wrong with your boyfriend. 1) An 'intimate text exchange' (sexting, right?) with 2) the widow of 3) his friend? Three reasons that are imo good enough to dump him - at least, if he doesn't have a good explanation/regrets it deeply.
I would definitely reconsider this relationship. Sexting to another woman is a first step to cheating. Sexting to a grieving widow is an whole new level of being an arsehole.