He was upset because he got rejected by a woman that he very much wanted to be his girlfriend.
"Hell hath no fury like a woman (or man in this case) scorned". - William Congreve.
And he certainly like her enough now. Because they are lovers now.
I think that being a sabbatical officer is fine for anyone wanting to prolong their time at uni for a year.
For everyone else it makes more sense to leave uni with their degree ASAP and move onto the next stage of their life ASAP - getting a job, starting their career, starting a business, travelling the world etc etc etc.
I think it's out of order for you to call her a nobody for a perfectly logical decision on her part.
The vast majority of students don't take up roles within the student's union. Are they all nobodies because of this? Of course not.
Are sabbatical officers worthless? No.
Its all about horses for courses. Each person making the decisions that are best for them.
I was calling Girl 2 an extrovert in the original Carl Jung meaning of the term:
Extraversion (also spelled as extroversion[5]) is the state of primarily obtaining gratification from outside oneself.
Introversion is the state of being predominantly interested in one's own mental self.
https://en.wikipedia.org/wiki/Extraversion_and_introversionExtroversion as in; focusing on other people and not on oneself.
Her being able to read the thoughts and feelings of others as she talks with them is a HUGE sign that she is extroverted because she's focused on other people and not on herself when doing so.
It's a hugely subjective statement of you to say that she is a dull person.
Even if she is, that could be exactly what your ex boyfriend is looking for. Someone stable to settle down with.
Your statement that you are more like your ex boyfriend than Girl 2 appears to be based on the entirely shallow basis of political views and friendship groups. I bet that if we were to look below the surface at the important factors in 2 people being happy together long term, we'd find that she is more compatible with him than you are.
All of this should be a hugely positive learning experience for you, that will set you up nicely for your next boyfriend - if you think calmly and logically about the whole situation.
Take the positives from all this and move on!