Hullo and welcome!
Do a tag search on NRE. Distance helps me a lot; not just physical but also virtual distance. Lose his number for a while!
Ask your girlfriend if she would want you as her lover. For me, threesomes definitely work best with the 'each in their own turn' principle, not simultaneously everyone jumping each other. If she is only mildly bi-curious, making out might be just the extent of what she desires with another woman, though.
"Resentment destroys more alcoholics than anything else. From it stems the root of our spiritual disease."
"In dealing with resentments, we set them on paper - list people, institutions and principles with whom you are angry. Ask yourself why you are angry."
"In most cases it was found out that our self-esteem, our pocketbooks, our ambitions, our personal relationships, including sex, were hurt or threatened. We were sore, burnt-up." Alcoholics Anonymous, 64-65.