I feel like I need therapy or something
You don't need therapy. You'll be fine as soon as you dump this headfucker.
He claimed sex with a condom was rubbish but I was aware he might be sleeping with others so was not prepared to do it without one.
Lovely. Trying to guilt you into condomless sex.
The last time we saw each other he stopped midway and said ours would have to be a platonic love because it just did not work in the bedroom.
Classic negging.
Maybe he has a problem & is covering up by blaming you.
Maybe he's a porn hound who can't handle real women.
But whatever the reason, this is downright nasty. No real communication, just a blanket proclamation that he reckons sex with you is rubbish. No accountability, no caring, no concern about getting right for each other.
This has flawed me completely because afterwards he was still acting like we were together and talked of our next meeting like it was completely normal.
See headfucker, above. Blowing hot & cold to keep you disconcerted.
Now I feel like sex is going to be a huge issue in any new relationship too and I just don't know how to process this.
See negging, above. He set out to make you feel sexually inadequate.
This isn't about you - it's about him.
The issues started to creep in around me waxing and him not using condoms but we were still really into each other and made the effort to keep things going. He seemed to have a very defined idea of what sex should be and sometimes it was great for both of us.
He sounds too inflexible to be any good in bed.
These defined ideas - are they porny? Did he get all his sex ed via screen?
It's the making me feel inadequate part I can't get over and now he's acting like it's no big deal.
Of course he is. If he acts like it's any sort of a deal he might have to be accountable for it.
He's being weird with you because he likes to undermine you.
You've known him 6 months. you think he's not over his ex, it was complicated from the start & he's a rubbish lay. It shouldn't feel like this. Get rid of him - he's messing with your head.