would you take a guy back if he left you for someone, then after two weeks of dating them come back to you, while only a week later you find out he was been sexting and hanging out with her this whole time?

i recently had been dumped for a girl my ex boyfriend has known for literally a month. He ended our year long relationship to date her. Two weeks after they had been dating he begs to come back, saying things like "i didnt know how amazing you were until i lost you". so i let him come back, now we weren't officially "dating" but we were still having sex, and pretty much everything else people do. then while he had left his phone with me she messages him, and i find out he has been sexting, and spending time with her this entire tme. he says he ended things on that friday, and i was learning all these things on the following wednesday. i have developmented anxiety and get panic attacks forcing me to relive when he left me, yet through all of this i still love him. im pretty sure i have made up my mind on what to do, but i was curious to what you would do in the same situation.