i think I did change my behaviour a bit to accommodate what he wanted but that was my choice wasnt it, it’s not his fault I accepted that. I think I just considered he was a decent man, decent job, stable home, quiet, not laddish etc. And I thought nobody is perfect and me and him did get on really well. I was early thirties when I met him too so I was keen to make it work.
Tale as old as time. I was exactly the same. And there's nothing about what you did that was terribly wrong - you were, perhaps, overly accommodating, but in the course of normal relationships, there is an expectation of give and take. You give happily in the unspoken expectation that sometime it will be your turn to be prioritised. With healthy relationships this expectation rarely even rises to the level of conscious awareness, because it doesn't need to - your turn does come, and nothing feels 'off'.
With dysfunctional relationships, your turn never does come, and when you start feeling that things are 'off', your mind makes justifications that allows you to continue seeing the other person in a positive light. You tell yourself that it's not them, it's a pattern you've fallen into, and sort of your fault. But if you bring it up, your partner will protest that there's no imbalance, or if it is, your expectation that it would be rebalanced by now is OTT because they've been going through a very hard patch, or you're being oversensitive. Or they promise to make amends, but the amends last only a short time before it's back to the same old story - them first, you second. Then the cycle repeats.
Part of the trouble is that there are a whole range of upsetting/weird/off/difficult behaviours that initially present in dysfunctional relationships. When you see each one for the first or second time, you see them as being discrete, not part of a larger character context of selfishness, lack of empathy, blame, paranoia, etc. So you give each of them the benefit of the doubt. It can take a long time before you start to see them again and again, and the pattern becomes clear.
Selfishness, false accusations of bad behaviour on your part, acting the victim and blaming you, heavy drinking, 'forgetting' the scan - they're all part of a larger pattern of poor emotional control, faulty logic and executive function, a mindset that externalises blame, lacks empathy and is self-centred.
Guys like this regard themselves as individuals who have to fight to be the winner in win/lose situations even with their partner (and resent it deeply if they feel they 'have to' let you win), and not a member of a couple who are both seeking win/win situations.