My partner has a bad habit of interrupting me 
Today we were having a conversation about something normal and trivial to do with work, which I began. He them says a few sentences about it, and pauses for a few seconds. During this pause I say something along the lines of "yes and I think that is why -" and I am them cut off by DP launching into another comment linked to what he'd said before.
He does this often, I have mentioned it to him and he says he doesn't realise he's doing it. He does it when we are alone also in groups.
It's started to irritate me, to the point where when he interrupts me I lose all interest in the conversation and give up talking. I've found myself rushing my speech when I talk to him as I am anticipating being talked over.
When it happens in groups I feel even worse!
When he stops talking I feel like saying "as I was sayinf......"
If I ever accidentally interrupt anyone, I apologise and ask them to continue.
Why can't he do this?! 
And breathe....