Being poly, your first relationship should always be with yourself (esp. in poly, you can't count on your partner(s) to always be there for you...they have others they have to take care of/want to be with as well).
So find a way to be happy on your own, whether it's a hobby or just going out somewhere on your own. The happier and more secure you are with yourself, the more others will be drawn to you (if, as it appears, you are looking for other partners). The more you seem to "need" someone, the less attractive you'll be to others.
Also, is there anything stopping you from getting to know your husband's girlfriend, at least as a friend?