Hey rocccks!
I’m in a similar situation, after a temporary break up I got back together with my Ex-BF and now we have split up for good.
The sadness part is scary, but maybe this “two step” break-up is actually a good thing: You know much more now about him, you can discard false hopes much more easily, and you have griefed a lot already.
At least for me it was not nearly as bad as the first time!

Some moments of sadness are inevitable, and they are also very valuable! The experience that you can nurse yourself through these moments, that you can accept, own and hold your sadness – this is what will make you much stronger and happier and more confident!
So invite them, let them come and rock on through them!
If you want to feel more safe you can make plans what you can do or what will help you in these moments, for example write an encouraging letter to yourself that you can read when you hit a low.
I have a no brainer yoga routine of only two or three movements that I repeat like a mantra if it gets bad.
However, most of the time I am surprisingly good! 😀 I had like 3 or 4 days where I was so sad I thought I couldn’t bear it, and I think they were only so bad because I was so afraid to fall apart and that I wouldn’t get things together again, so I kept fighting the feelings. But alas, nothing happened and I am feeling much better!

I am pretty sure with your friends from University and so much to look forward too you will be fine, if not awesome, and some days or maybe even a few weeks of sadness will not thwart that, but they might actually contribute to your sense of self compassion! So roccck on! 🙂