<human>: Can you summarize the given text in a few sentences?

All right, first things first let me give background information, my ex (call her 'B') and my current (recently made ex? Call her 'G') partner were friends before I knew either of them met and I met G through B. I dated B for about 6 months but things fell apart and we split up.

After we split up B proceeded to spread rumours amongst her friends that G and I had been fooling around her back. We hadn't. The two of us (G and I) were alienated from that group and grew closer because of it and after about a month we decided to give it a go and started going out.

Things between us had been awesome, and out of the blue B messages me and says she wants to get coffee and some of my things she still had. I headed over to her place and we had a chat, I grabbed my things and was about to leave when she kissed me and tried to go down on me, I didn't resist initially because I'm an idiot but I quickly came to my senses and gtfo'd out of there.

Further adding to my stupidity, I didn't tell G about this because I knew it would cause a shitstorm and I just wanted B out of my life. fast forward a few more months and G gets a message from B asking if she wanted to get coffee, G said all right as she didn't see the point in harbouring a grudge.

After a few hours of expected radio silence I get a text from G that reads, "you lied, its over." She told me she still loved me but that it was over between us. I assume this is about the time I went to B's place because other than that I haven't been in contact with her at all.

I don't know what to do right now, I'm historically not a very emotionally stable person so I'm trying to keep it together and figure out what to do/say, someone please help me.
<bot>: My current partner broke up with me after having coffee with her ex who is a mutual 'friend', I don't know why but I think its because my ex tried to go down on me and I hesitated in stopping her.