the trouble with marriage is even if you know the person really well people change over time. the person you marry today is not the person you divorce tomorrow.marriage is good if she's from a different country and you want to be together but immigration peeps are a problem. In some countries you can be subject to a "common law marriage" but thankfully not the uk.
If you get a Thai bride do not under any circumstances purchase property. under Thai law only Thai people can own property so she gets it by default