no one says he is a monster
@Littlewing80 Not a monster, as unfortunately sadistic twisted men obsessed with sex are not unheard of. But a nasty creature.
Straight after the panic attack/having sex thing, he asked what had caused it. I talked about it (it was to do with my ex), he listened, he held me, he looked after me.
They do, it creates the process called trauma bonding. For instance, a man who has hit a woman will tend her wounds afterwards and kiss her etc. He did not treat you well, and he knew that- it was a violation and you know that, that's why you posted about it at the time.
After the abuse the abuser knows he has to win his partner round/gaslight her into thinking he isn't what he's just shown himself to be. He is the only person there to comfort her immediately after a traumatic experience, and so it creates trauma bonding/Stockholm syndrome. www.talkspace.com/blog/trauma-bonding/
What you describe is horrible to hear OP, how you are in the thick of it, you still believe he is sincere.
I actually thought he looked like he was about to cry.
Yes, my ex could also fake tears or fake being on the verge of tears. They do it to make you believe they're truly cut up that they hurt you. But it's all manipulation to keep you hanging on.
When as he was leaving he said something stupid like 'you have no idea' and just left.
I hope you are starting to get some idea. Not a word is sincere with these guys, or we will never know what is a throwaway comment and what is an attempt at manipulation. With this comment I think he sought to leave you on a 'cliffhanger' of anxiety worrying what he meant, to add to the impact of the blow he was planning to deal about his cheating.
He sent this long email about how it was hard for him to hear about my anxiety etc as he cant fix it. He likes to be in control and he cant control this which puts him out of his comfort zone. He then admitted what happened with the fwb.
I.e. he said he doesn't really want to hear about your feelings, because it upset him and might lead to him cheating, as might him having to leave because your kids are coming home and they are still your top priority thankfully, not him. Unfortunately, a lot of women end up that these men become their top priority even above their children, because of the emotional manipulation.
But what is this?
Manipulation, psychological and sexual abuse/sadism. Part of your feeling of wrongness is 'cognitive dissonance' www.thenarcissisticpersonality.com/cognitive-dissonance/ because you're trying to convince yourself he's a nice guy, when his behaviour shows you he's not (nice words are easy to say, especially when they get him what he wants.)
^Anyway, I've emailed him. Said some of how I'm feeling and that I need a break to sort my head. Not the end but I guess it's a start.
Thank you for listening to all this shit and your advice^
Well done OP, keep going please! I will be delighted to hear when you have left this sicko behind for good. I'll donate to a charity of your choice. 
He's told me that if I really do feel that way about him then he agrees we shouldn't be together as he doesn't ever want me to feel that way. So I guess that is it for now
@Lorelai101 This is all manipulative shit designed to screw with you and convince you he's oh-so-adorable and selflessly has your best interests at heart. Please block him on your phone, Facebook, email, everything. xxx