16 month will no longer sleep in cot

[Help78]

Our 16 month old used to be a perfect 12 hour a night sleeper and went down with no struggle. She had a spell in hospital over Christmas for 10 days followed by another night in hospital a few weeks later. During both times she slept in a big bed with one of us. We had bedtimes back to normal but had night waking where she didn't like being on her own. I was beginning to settle her ok but then I work away 2 nights a week and my partners solution is to put her in the double bed in her room with him. I sought advice from a sleep expect who helped us at 6 months who suggested taking the side of her cot off as she might be ready for a big bed. This was a disaster as she then wouldn't go to sleep on her own and kept falling out so we put it back on. Now she won't go to sleep without one of us holding her hand and the past 2 nights won't go to sleep at all on her own snd gets upset to the point of coughing and being sick.
It's weeks now since my partner and I have gone to sleep and woken up together.
I bland him for always sleeping with her and he blames me for listening to the wrong advice about the cot side (which I've admitted I was wrong!). All in all we have a baby who's separation anxiety is pretty bad but also she's clever snd knows if she cries enough she'll end up in the big bed.
I have no idea what to do as my partner thinks it'll pass and that I'm obsessing but I fear our relationship may end over this!