There's too many unknowns at the moment. There's still discussion if XMRV exists, let alone if it causes disease. So transmission routes are unknown as well.
What we know of other retroviruses makes it likely it is spread by sexual contact however. The Belgian CFS doctor Kenny de Meirleir has made claims in that direction as well. German research also makes it more likely that XMRV can be spread by saliva (finding XMRV in respiratory secretions). There's also been some research that found 50% of family members were infected with XMRV I think, which could also mean it is spread by saliva. We know from retroviruses infecting animals that saliva is a possible transmission route.
For now, nothing has been proven yet, though. And many of our partners aren't ill, even after decades of intimate contact. It might turn out they have been infected with XMRV, but so far they don't seem to suffer from it... Now, there is the other side of the coin of course: there are patients who are reporting their partners and children also got CFS.
At the moment I think there's just not enough data to come to any formal conclusions.
To be on the safe side we could live like hermits I guess... but XMRV has also been found in up to 7% of healthy controls in one study. This means it's going to be hard not to come into contact with this virus. The cat's already out of the bag.
It's a dilemma, but if I were in your shoes, I wouldn't let the current state of affairs hold me back.