I put a programme like this together for "A university somewhere near London".
The only way I could see the workload making sense was to do the PPL during or prior to the first year, ATPL groundschool during the long summer vacations, starting about 2 weeks after exams, and finishing about 1 week before start of term (you need some break!).
Doing the degree and ATPL work at the same time was just never going to work. But this way, with intelligent phasing, we reckoned you could finish your groundschool exams about 3 months after graduation - but there was little slack.
Hour building could potentially be a leisure activity during the undergraduate degree, or after the groundschool had been finished, but needed to be done in a way that didn't interfere with the undergraduate studies.
Realistically, you are probably looking for a couple of short holidays with your GF annually, and hopefully persuade her to come and live with, or at-least very near, you during her summer vacation. It'll be tough on the relationship, as well as tough on you - but if you get to the end of it all intact, pretty much everything will get better thereafter! You'll also have an impressive capacity for continuous hard work!
G