He hasn't been physical with someone else, just online discussion. We have been involved in BDSM for a while but only played with each other. I've done a lot of reading and discussing having a second sub with other subs and doms and reading on certain kinks he has. I know he wouldn't have a problem with me watching him be with another sub but I would be uncomfortable. Thinking of him connect with another person that way makes me feel very inadequate.