Started 'dating' guy bestfriend only to find he was still chatting up his ex...

Alright so me and my bestfriend started ‘unofficially dating’ mid-January after he started showing feeling for me in November. I was reluctant at first because of our friendship but he seemed sincere and won me over. We started displaying our affection for each other to friends and family recently but then I told him I wouldn’t kiss him or be all over him again until he officially asked me out. However last week something happened where his ex texted him saying bad things about my girl bestfriend. I told him I didn’t mind him being friends with his ex. I knew he had some lingering feelings for her [they had gone out for 3 years and been broken up for 6 months] and I thought to really get over her he had to walk away on his own. He told me it was her who was having a hard time letting go and he was trying to talk to her as little as possible and I trusted him. So hearing that they text each other I got a real bad vibe. I asked one of my friends who talks to his ex to dig a little for me. I found out the text on a daily basis and I confronted him on how someone he was trying to get him to leave him alone he was keeping a pretty open line of communication [he had gotten a new number so she either asked for it or he gave it.] It only got worse when I found out what they were texting each other. His ex told my friend that he was texting her things like ‘I love you’ ‘Everyone knows me and ___ aren’t going to work’ ‘She’s not my type’ I want to marry you’ ’she means nothing’ and things of that nature. I told my friend that forwards could be faked and she needs to see them on her phone herself and she did the next day and it was all true. I confronted him and said everything between us was done. He promises to never talk to her again even as a friend and that he only felt that way when they talked about the past and he’d say the things he used to and when that didn‘t happen all he thought about was ‘us‘. I told him if he needed a break to sort through his feelings he could’ve told me and that I get why it’d be hard. He apologized so much I almost forgave him until he said he didn’t come to me because he didn’t want to hurt me and lose me. I told him that saying that was insulting and if he was so scared why did he keep doing it. He said he didn’t know and I responded by saying that’s what hurt most was know that at that very moment, if I didn’t catch him, he’d be texting her ‘I love you’ and that I meant nothing. Since then I haven’t acknowledged his existence. Because we were friends, we are sort of apart of a group with other close friends who we do everything with. Now he keeps to himself and barely talks if no one talks to him. One time after the movies, I was being loud and having fun with friends while ignoring him, we were driving around he abruptly asked to be taken home and his voice was shaky like he wanted to cry. He keeps glancing at me but looks away when I turn my head in his direction. He’s been going to one of our friend who helped him win me over in the first place and doesn’t know she tells me everything he says which is him beating himself up, swearing to never talk to his ex again, saying it was a mistake and asking for more advice. It’s starting to work and I’m starting to miss talking to him. Every time I come close to forgiving him though I replay the words I read in my head and it hurts all over. I want to forgive him but I also don’t want to feel like an idiot because I do feel played. I also would only want to be with someone who makes me feel special and right now I feel like 2nd best to his ex but he swears he realized that I’m the better girl. His ex is a shitty person, she flirted with all his friends, while making him cut contact with all his female friends [though he’d talk to me regardless] and anyone she didn’t like and I don’t for a second doubt she poked and prodded at his weak spot because she just that kind of girl who likes to manipulate people and has always tried to dig her claws back into him when he showed signs of moving on. I’m not naïve, I know his feelings for me were nowhere near what he felt for her which tempts me to be more understanding in this. Yet I still feel he had the responsibility of being considerate to me and show some control. Everyone in the ’group’ wants to keep out of it so I can’t go to them. I already know IF I do forgive him a clause is that he cuts off all communication with her and I want to see her number isn’t in his contacts. We both know I’ll find out if he lies again because his ex gets mad at him for every little thing and would go to the same friend who told me this time and who would tell me in a heartbeat because she can’t stand him. I’d just like some advice on what to do, if he seems sincere and if I should forgive him because our ‘romantic relationship’ didn’t just take the hit, but also our 4yrs of best friendship.

I know this was long so thanks for taking the time to read this and I appreciate your input.