Than you so much for your answers!
Basically, before he proposed and I moved in with him, we were always living in different cities and mostly even in different countries. I was studying and moving about quite a lot, he was consistently in one place. We got to know each other 9 years before we married - we went out for a while, then he had second thoughts and broke everything off, then had more second thoughts and re-established contact. This happened quite a few times, and because I really, really liked him I did not call it quits. I simply thought that I was still not settled anyway, so if it was meant to be, it was meant to be.
5 years into this on-off spiel, he decided to become a permanent fixture in my life. We went on holidays together, I met his parents (he'd already met mine), we talked every day. But - as I found out - this apparently did not translate into him being exclusive with me. He was always very reluctant to be referred to as a "boyfriend" or partner as well. And he did every so often go into a whole lot of reasons why we are not compatible, so I did not feel particularly secure in all of this. But - going with my brilliant philosophy - I went with it, because if it was meant to be blabla, and also because of the classic "it will get better once xyz has happened".
So - in the end, he did propose and I fell pregnant, and we married. However, this did not end my insecurity. Even though he claims that he is "very happy" and "should have married me much earlier", he did not explain his long, long reluctance to commit...and I'm still very, very hurt, because in the initial phase, the way he broke up with me on a few occasions was rather like a rude dismissal (say, via email!) - which was also never really talked about.