It is also not a good thing to think that only other HIV positive people would be interested in you. Thousands of people are in happy and safe mixed HIV status relationships.
But some people with HIV prefer to have relationships with other HIV positive people. It might seem simpler and feel more comfortable when a partner knows what it is like to have HIV. There are also no worries about infecting the other person, although there is the issue of re-infection to consider. And you might see no need to use condoms, which could be important to you.
Of course, we should never assume that a partner has HIV unless this has been shown with a test. It can be easy to assume that you both must be HIV positive but only a test will tell you for sure.