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

Have been with my GF for 4 years now.
Dated exgf for about a month 6 years ago. She is also currently in a relationship.

GF is best friends with ex however I have had very little contact with her over the last few years, probably due to GF feeling uneasy about it, (quite rightly.)  

GF asks me to help exgf get a job.

Ex and I start talking about the job and then just generally a bit more. 

Slowly feelings start coming back/forming, (this is where it should have stopped.)  We catch up a few times at work on a break etc and briefly talk and there was obviously a connection there.  End up catching up outside work and just sitting in her car talking for awhile.  

One thing leads to another and we briefly kiss.

I know I need to break up with her and sort my shit out. One problem here is by coming clean I ruin about 4 peoples lives.  The other problem is I seem to have developed feelings for the ex, we have tried to cease all contact however don't seem to be able to.  We just get along really well and are talking over how best to handle this situation.  We have agreed that catching up again is completely out of the question.
<bot>: Birefly kiss exgf who is current gf's best friend.  I have no idea how to best handle this.