Fusing

I'm part of a multiple system, and I was wondering about people's successes (or lack thereof) in fusing or integrating with one or more of their bodymates.

I fuse with Angel sometimes, which feels good while it lasts. We're more comfortable in our body as a fused entity then either or us are on our own. But it's not feasible or desirable as a permanent structure.

What have been your experiences, and the experiences of others in your system? What causes them to fuse? What causes the fused form to disintegrate?

-Baki