I think it can be easy to get caught up in the drudgery and work involved with having children, working, shopping, cooking etc and to end up not having much time for each other.
We go away together when we can and it's wonderful. We don't bicker and get stressed much really even when our 2 children are here mainly because we have more or less sorted out domestic/children responsibility and share it fairly evenly I'd say. So although I do loo rolls, dh does bins and collects both children every evening. What are you bickering about? Is it chores and childcare?
Having 2 can be harder but for us, it was just the first 1.5 years that was harder than having 1 and then only because dd didn't sleep. So lack of sleep (adn we shared it, dh got up every other night so we both got a good nights sleep every other night) made that first bit v tough. Other than that I love having 2.
It helps having some money to throw at the problem of not having time together, Sitters babysitting agency is excellent and we've used them quite a bit so we can go out to dinner together. I also have a brilliant ex mil who will have both of them so that helps and means we can get away to a hotel for a couple of nights. You can get bargain hotel rooms here, at Laterooms
I think other things that help us are having a cleaner (so we don't argue often about chores/housework), shopping online, paying bills by direct debit so it's no-one's responsibility to pay them, having good childcare while we work and a good routine about who drops and collects children (I drop ds, dh drops dd, and then he collects both in the evenign as I work later than him) and making sure that we make time to talk to each other. Sometimes we come in from work and go straight to our room for a chat. So I don't think 2 children has to strain a marriage any more than 1 and there are things you can do to make life easier. HTH.