The universe bought us together but he has betrayed me for an emotional affair with his ex several times

Me and my partner have been together for 14 months, we met in the most peculiar way and it really was love at first sight, I didn’t believe in that till I met him and looked into his eye, it was as if time stood still and we both recognised each other. We both, with no doubt in our minds truly believe the universe bought us together and we have certainly met in a past live.
Anyway the relationship as you can imagine went extremely fast, we was living together within 4 weeks. I’ve never loved anyone more, I’m 34 and not long got out of a 7 year relationship when I met my current partner. He was just everything and still is everything to me. He does a lot for me and treats me well, he would be absolutely perfect for me if he didn’t betray me for his ex, several times!….
So they were together for 8 years, knew each other for 18 and once she found out he had moved on she opened communication gates with him, emotionally black mailed him (I’ve read all the emails (yes emails)) and she seems to have this kind of hold on him where he completely forgets where he is and who I am, the first time he responded was about 6 weeks after we got together and he said some negative things about me and told her something very personal about my son. As well as “I love you” “it’s always been you” “im saving up and leaving” (he wasn’t).
I found out through her, she facebooked me, found my music Facebook page and msged me on there, as well as finding my email address and emailing me. She recorded the conversation they had over the phone and sent it to me. She said some really nasty things about me, she doesn’t even know me! Never met the girl.
Anyway he said he was just appeasing her cause she makes him feel bad which is possible cause he’s weak. however this has now happened 4 times. He’s told her “it’s always been you” “ we ain’t going to last much longer” “I miss you” “I wish I could hold you” I know what you’re all thinking…why didn’t I get rid of him? Sometimes I wish I could cause this hurts like hell, however I know this man, I’m not brainwashed I have questioned whether he is a narcissist and love bombed me but I know he isn’t, he has so much empathy towards people and often puts others before him, he does a lot for me and loves me in a beautiful way. After the last time this happened whenever I bring it up he speaks about her in an angry tone which he didn’t do before, he’s also much more transparent with me so I believe there was still love there but now he’s over her, I don’t think he will do it again however I’m so paralysed with what’s happened that I’ve constantly got a gut feeling like he’s speaking to her again, I’m now possessive, I check his phone and the trust has completely gone.
I keep telling myself “he didn’t leave” not once’s did he leave and go to see her when she was begging for 24 hours with him! (Again seen the email) that’s what makes me feel a bit better about this crippling situation.
I truly believe he is over her but I can’t get over what’s happened. It’s made me ill I’ve never been so hurt in my whole life, and I’ve had a a hard time on this earth like a lot of us have.
I absolutely adore him and Believe he adores me but at the same time how could he? He’s my home and my safe place but at the same time I’m terrified of him cause I know what he is capable of.
We’re going to start therapy next month which he is pushing for as well as me, that brings me comfort cause I know the ex was trying to get him to go counselling for his shit childhood and he never went, We went twice after the second time this happened.
This has put such a toll on our relationship and I just want us to be happy. I need to get over this and forgive him so we can move forward I just have no idea how to?
Thank you for reading I would really appreciate success stories from people who have been in similar boats! But comments from anyone is of course welcome. I just need advice on how to get over this.