I vote stay out of it. This isn't just a situation where a friend is in trouble and you're in a position to help. A crime was allegedly committed here and the OP's boyfriend may be involved, ultimately, in either a criminal or civil action involving it. For that reason, don't complicate it further by interjecting yourself any further. One possible scenario: You tell her your concerns and then she confides in you something even more damning or incriminating about her husband and, god forbid, admits that she was somehow involved. Then where are you? Leave it to her cousin to intervene.
Live with intention. Walk to the edge. Listen hard. Practice wellness. Play with abandon. Laugh. Choose with no regret. Continue to learn. Appreciate your friends. Do what you love. Live as if this is all there is.
--Mary Anne Radmacher