What Else Could I Do

It started about six months ago when my gf talked me into licking my own cum from her hand after a good long hand job. As it made her giggle so I humoured her and repeated the humiliating act every time we made love. She particularly enjoyed the first time I licked it from her pussy, her hand on the back of my head so I couldn't back out. Last night I was forced to watch her fuck another guy me underneath watching her penertrated. He moaned he was about to cum, she spun round and placed his pumping shaft into my mouth the spunk hitting the back of my throat making me swallow, they both laughed. What am I going to do? I'm straight but don't want to lose her,I love her