Your fear is completely understandable. But hopefully you’ll look back and wonder what you were worried about, as is often the case.
I remember looking at all the pills I had to take and thinking ‘so this is what it has come to’. But Mtx helped me quite a lot and I’m one of the lucky ones who experiences few if any side effects - I’ve been taking Mtx for over 6 years now.
I’d be really upset about, well, everything to do with the disease if I had young children to care for. It is daunting, nobody would say otherwise. But please remember that it is often those of us with particularly stubborn symptoms who tend to post here, there must be many, many others whose PsA is so well-controlled that they’ve not really got much to say about it. You may yet join that fortunate band.
Keep looking to the future. I think getting over the hump of the first ‘serious’ med is a real step forward, especially if it brings significant relief. And if you do have problems with Mtx, then you & your rheumy will doubtless decide to try something else which would be another step towards ‘the’ drug for you, the one that will make a huge difference. Good luck Mwitt.