I'd say you have to find some space in which to grieve the end of the relationship with Ted, first--and that means away from other love interests. It's not surprising that Craig is willing to provide support; the support you need, however, is time and space away from that relationship to work through the worst of the grief from the other.
So find somebody else to talk to about it. Limit the time you spend with Craig to an amount where you know you can be present for him and avoid unwarranted criticism and grumpiness.
Then evaluate what you want from relationships in the future and figure out how Craig fits into that. It's not for you to tell him to find other people to date, though. You can only establish boundaries as to what you will and won't do--he has to decide for himself what he's going to do in relation to those.
When speaking of various forms of non-monogamy...it ain't poly if you're just fucking around.
While polyamory, open relationships, and swinging are all distinctly different approaches to non-monogamy, they are not mutually exlusive. Folks can, and some do, engage in more than one of them at a time--and it's all good.