need some advice please

my SO and I have been together for a little bit over a year, we got sober together and we've been through hell and back together. he relapsed on thanksgiving and i left until he decided to get sober again and he seemed like he was really changing. i forgave him for his past transgressions because i hadn't been perfect either, i never cheated on him or anything but he would lie to me about going to hangout with girls or talking to other girls or watching porn (I've had a bad history with men so i am extremely insecure and dont like porn) anyways, he's been in jail for the past month and a half because of some things he confessed to about doing before we got together and he's looking at doing at least 5 years, but i truly love him with all my heart and told him i didn't mind waiting because i felt we were meant to be together. anyways, I've had his phone since he got locked up and found out he had been talking to girls right before he got locked up saying he wished things could have been different when they were trying to be a thing several years ago. now I'm his first official girlfriend so ive given him chances because he said this is all new to him. anyways, i was pissed because he lied to me about it AGAIN. well last night i messaged a girl because i heard he had been fucking her for the last couple months while we've been together, i told her i wouldn't be mad at her but i just wanted to know the truth. he had told me he drove her around for a couple hours in February because they work together and she was really struggling or going through a hard time i guess he told me nothing happened but then she told me THIS.

so he left out the fact that he asked her to fuck, i dont think she's lying, she has no reason to. my heart is just broken I'm not sure what to do. since he got locked up he told me he realized how stupid he was and how much of a catch i am and how perfect i am. I'm just so conflicted i love him but I'm so scared ill wait for the next five years and he just do this to me all over again and I'll have wasted all that time. please try not to be negative because I'm having a hard time with this as it is. please i just dont know what to do.