Okay so you should tell Myra a few things in this order :

• You felt bad for Pat as he was still depressed after their breakup.
• You were not flirting, as you have a gf right now. You friendzoned him as clearly as possible by calling him "bhai".
• He probably texted Myra the "tell her to stop flirting" to make her jealous. It must have been a desperate and deplorable attempt to win her back somehow.
• Tell her you won't talk to him anymore, as he clearly is manipulating both of you.
• Myra should apologize for the slutshaming and the homophobic insults.

If she doesn't believe you, you can send her the conversation with Pat, and tell her to f*ck off until she apologize.

In the same time, you should tell this to Pat :

"Did you mistake my pity for interest ? I was never interested in dating you, i considered you my friend, no more, no less. You tried make Myra jealous, thanks to that i might loose my best friend, my girlfriendAND my reputation. I want you to apologize to me, and to Myra for your pathetic behaviour. Have a good life."

Then with your gf : she is an unfortunate casualty of Pat's manipulation. Tell her you only like/love her, and ask her if she wants to read the conversation. Whatever she choose, screen her the last message you sent to Pat.

Sorry this was long, hope this gives you ideas. Good luck. I hope thinhs with your gf will get better, and i hope Myra will apologize.