Thanks for the responses, I agree I should not jump to the conclusion that I need to leave the relationship.
To add more details, I'm doing graduate work in another country. I've been going back and forth for about 2 years now. We use skype to see each other and work everyday. It somedays feels as though we maintain all the elements of a relationship without the sex (all the work non of the play) so when I am finally on leave or on camera I just don't feel sexual.
With the partner I am having the disconnection with I raised this issue with him a year ago and he's been very patient, he's not feeling a disconnect towards me.
When I have difficulty performing with him I just find my mind shifts to concern about whether or not I'll be able to perform, why can't I do so etc...and I just get so anxious I now avoid even talking about sex. Whereas the other partner does not illicit this response.
This is especially challenging because my time overseas is about to end and I will be coming home for good soon and I am extremely happy yet really nervous about what will happen.
Hope this has given more info clearly, thanks everyone