Complicated Situation -- Marital Status

My visa situation should be very simple, but it has become very complicated. I am a US citizen in Germany. I am applying for a Tier 5 Temporary Work (Government Authorized Exchange) visa to take up a work placement in the UK.

On my application, I put that I was an "unmarried partner." My boyfriend, who is a European citizen, and I have been together for several years and have lived together for almost two years.

After submitting my application, I discovered that I might have to provide evidence of my unmarried partnership.

I would be exceedingly grateful if anyone here can help me figure out the answers to the following questions:

1) Do I really need to provide evidence that my boyfriend and I are unmarried partners even though my boyfriend is a European citizen and not coming with me and even though we are not applying for an unmarried partner visa?

2) If so, what kind of evidence?

3) Here's what the VAF9 guide says about the "unmarried partner" category: "You currently live in a conjugal or marriage-like relationship with your partner but are not legally married." I honestly thought that described our relationship when I submitted my application. However, I've since read things elsewhere to suggest that I probably should have listed myself as single. Thoughts?

Surely you are applying under Tier 5 so you're not applying as a partner of an EU national. The 2 should be separate. If you were applying as a partner you would have to provide proof because that is the whole basis of your case for the visa. If you score the points for Tier 5 exchange you should not need to prove anything else.