I feel so trapped!!

The title says it all. Idk what to do anymore i feel like im stuck right now. I recently found my fiance was still buying pills off people behind my back because of his “back pain” when quite honestly i think hes just being a little bitch. We both have a herniated disk, do you see me taking shit every day for it? No. Iv had mine for 6 years. Doctors prescribed in the first place which started this issue and growing up in a household of drug abusive parents im not about to marry it. I explained i was not going to tolerate this and i will end the relationship over it, he stopped. Apparently. Now his phone records show hes been calling this guy the last two months and i told him yet again i WILL NOT tolerate drug abuse. Iv been with him for 5 years and im fucking over the lies! Hes lied about previous shit in the past (different issues) and we did premarital counseling because im sick of putting my trust in him to be honest. This is the last straw, iv literally lost all sympathy and don’t even have emotional connection to him right now no matter how much he tries to apologize and make it better. Im done. Im so overwhelmed. Our jack and jill is literally this Saturday which my grandmother has dished out over $6000 for already and wedding is Oct. i just found all this shit about the pills 2 days ago. I do not know what to do with myself. Id feel like absolute shit calling off everything after all the money shes paid and cant get back. I love him to death, but i feel no connection with him after breaking my trust this last time. I dont want to marry a fucking liar. I feel like i cant breathe.