Hi, thanks for your question. My name's XXXXX XXXXX I'm going to help you with it.
If the order simply states "full time education", it will not be clear whether this includes university education. It would therefore be advisable to check the precise terms of the order, as some orders specifically define full time education as "secondary education". If yours includes this definition, university studies will not be covered and your liability under that order will cease when your son leaves school.
Until that time, maintenance will still need to be paid to your ex-wife.
Nevertheless, if there is no assisitance on the definition of "full time education", and you cannot reach agreement with your ex-wife, then the court may need to decide this. Of course, if your ex-wife delays in making her application, and, in the meantime you make arrangements with your son for financial support throughout his university education, then it will make it difficult for you wife to gain the court's sympathy that the order should continue.
If it does go to court and it is decided that the order should continue, you should be able to secure a term of the order that, once your son leaves school, you will pay him directly, not your ex-wife. The one caveat to this is that the court might order an apportionment of payment between her and your son, to take account of periods outside term time when he is at home.
The income of your ex and your partner is not relevant to your maintenance obligation under the previous order but yours is; so if you have, for instance, suffered a material reduction in your income, this should be brought to the court's attention if and when your wife makes her application.
Please don't hesitate to let me know if any of the above requires clarification. If my answer was helpful, please also remember to rate my answer as it's an important part of our process and is the only way I can obtain credit for my work.