First, I'm sorry for the situation you're in. My advice to you is to divorce this woman as soon as possible.
The size of your dick doesn't make you the man you are; your actions do. What you're doing is casting your dignity aside to indulge the selfish, manipulative and childish whims of a GIRL who knows exactly how to get what she wants.
As long as your dick didn't shrink since you started dating, there's nothing that truly changed except for her realization as to how much she could exploit you. She realized she could have it all: a handsome boyfriend who would pay the bills and dote on her while getting action from so-called "real lovers", going so far as to humiliate you in front of these other men, multiple times per week in a house and on a bed that YOU, my friend, pay for. These aren't the things good relationships are built upon.
Ask yourself how much longer you're willing to accept this appalling behavior -- from her, but more importantly from yourself. The truth is that your wife, this girl, is abusing your decency -- your willingness to commit, to love, nurture and support -- and doesn't deserve a second more of your time.
Divorce is ugly, and it's likely she'll kick and scream when she realizes she's losing you. She'll dig her claws into you, and when that doesn't work, she'll try to destroy you.
Therefore, it's absolutely important that you begin DOCUMENTING EVERYTHING.
Read up on one-party consent laws (http://www.citmedialaw.org/legal-guide/recording-phone-calls-and-conversations) to understand your rights and legal implications for recording in-person and telephone conversations. You may not need to notify her that you're recording.
Record the conversation between you and her when you tell her you'd like her to stop fucking other guys (I assume you do). It's likely she won't, so take note of (and possibly record) what happens after. If you can't record, transcribe from memory. These will serve you well when you show up in court. From this moment on you need to be smart; this isn't just about your girlfriend with those guys upstairs: this is your life.
Best of luck.
