Ofmice: I think it comes back to knowing yourself. This can only come from experience; we have no knowledge of our responses in sexual relationships until we've had some! Sharing experience is also very helpful, ime.
I didn't understand how readily I love, so couldn't see that loving XH wasn't a good reason to plug away at the relationship.
I didn't know my 'like' radar is more finely tuned than the 'love' setting, so I need to pay close attention to its findings.
I didn't understand I was being abused or that I was conditioned to keep trying harder to please abusers, so I blamed myself for my unhappiness.
I've been conditioned not to expect secure happiness, and to mistrust it if found, so didn't realise my relationship wasn't good enough for me.
So, yes, you will see me saying relationships shouldn't be hard work - and that happiness is not a right, but we all have the right to walk away from unhappiness. I also encourage others to 'listen' for their gut reactions, to look for evidence that they're 'being' loved as well as hearing and feeling love, and to seek benchmarks for good relationships.
Six months of doubt, fear, dullness, anxiety, revulsion, contempt, mistrust, disappointment, loneliness or eggshell-walking is approximately four months too long. Even if there are external reasons for the misery, a relationship which cannot negotiate successful coping strategies is not a good one imo.