A few people have discussed this, but as an ex-expat trailing spouse who went through it, i can't emphasize enough that you MUST find out your legal rights with regard to your children and possible separation/divorce.
I was pregnant when I followed XH to the US, and of course didn't go thinking he would have an affair with a colleague while on numerous lengthy business trips, help little to none with DS when he was home (he was entitled to 2 weeks paternity leave but refused to take it, never got up in the night with him once til he was about 5 years old but wondered why i was always tired from lack of sleep, couldn't look after DS by himself without calling me to find out when i was coming back and on and on), or that he would prevent me from returning to our home country with DS, or that he would refuse to let us leave unless i accepted reduced child support while restricting us geographically to pretty much the most expensive city possible (while he's on $250k salary). even when separation was first being discusses, XH of course spouted nonsense about how he wanted to do the right thing...
All these pp who state outright that they would never be with someone who could do that - that's exactly the point, you never know how someone is going to react to that kind of situation. I was sitting on my high horse until it happened to me too.
I ended up trapped in the US for a year more trying to get divorced and permission to leave with DS because XH turned spiteful because I dared to leave him. my legals bills are at about $80,000 and i'm not done yet as he is trying to prevent me from getting my share of marital assets that have been ordered divided.
if i did not move money when i found out about the affair, i would also have gone into serious debt to get divorced as he immediately emptied the joint bank accounts and moved his payroll as soon as he knew it was over. as one pp said, if you do go, make sure you have a getaway fund just in case - if it never gets used, great.
And from the outside, I also had a "lovely" life, funded by his job. Except he would not have the benefits of that lovely life and the time/energy to devote to advancing his career (at the expense of my own) if I hadn't done literally 99% of our life admin and 100% of childcare.
in addition, once you yourself become ordinarily resident in a country, your marriage/divorce potentially also becomes subject to that jurisdiction, i.e. you may not get as favourable terms as in the UK. and that is entirely dependent on where you are moving to (within the US, it varies even state by state).
I realize this is worst case scenario, but I really wish I had known to at least think about it before I moved, instead of being blindsided.