i (f27) found by boyfriend (m32) texting another girl again and i want to leave. what might be my best exit strategy?

background info, a few weeks ago i found texts in my boyfriends phone, telling another girl that hes going to marry her, as well as telling the girls friend the same thing. there was also something brought up about spending the night when he goes out of town for work. he claims the texts were nothing and that theyve only ever just been friends. well, that work trip is this week tuesday- thursday. so yesterday, he left his phone open and i looked at his texts. he was texting another girl, but when i looked at the texts, they were all deleted except her last text that said shes down to meet up sometime and that shes free most weekends. obviously there was something to hide if the rest of the texts from yesteday were gone.

anyways, ive had enough. i want to break up with him and be done, but we live together and we just got a bad snow storm yesterday with a bad cold front coming today. id be the one moving out because i cant pay the rent myself. ive been wondering how i should go about breaking up with him, he leaves tomorrow evening (tuesday) for his work trip. i dont know if i should break up with him tomorrow before he leaves and move out while hes gone, or if i should break up with him today (monday), spend the night at my parents, and move out while hes gone. how would you go about leaving in this situation?