Monogamy no.
Long-term romantic commitment (between two or more people, with or without sexual exclusivity) very very much yes.
This.
If we have come to accept, after centuries of denials, that genuine feelings of love can emerge between two people of the same sex, I don't think it's much of a stretch to assume that it might be possible for a person to develop genuine feelings or love for more than one person at the same time.
Obviously, "polygamy" as practiced in modern days and in history, is something disgusting and generally oppressive toward women. So voted yes.