great topic! this is actually the point of conflict that my husband and i are having right now. we made poly agreements when we first started dating. we dated some people (some serious, some not). then his girlfriend moved in with us and although she only lived there for a few months, i realized that i LOVED having her merged into our lives. during this time, my boyfriend was also around most of the time and i discovered that i really REALLY liked having more than 2 people in the household.
fast forward 6 months: girlfriend has since left the picture and after a series of progressively worse and worse breakdowns from my husband, it has come out in therapy that he can't really handle any kind of "merging". he wants us to just date people and starts to become very uncomfortable if signs of them start creeping into "our" life together. we are currently in therapy to determine if there's a way around this conflict, since my boyfriend was still pretty integrated into our lives (boyfriend has since taken back his cat and all the "stuff" he had at our house in an attempt to help my husband through this). depending on the extent of our differences on this point, we may end up splitting up.
so yeah. i'm a merged person. i like having someone or someones who i'm merged with, i like seeing them merged with other people to the extent that it's possible. it makes me happy and supported, like everyone is working together as a team (assuming things are going well!).