I need desperate help!!!!

I'm speaking with this guy and when I saw him the other night, he was very flirty and touchy in a respectful manner, he is seeing this girl he has been trying to date for a couple of years but she doesn't want anything, so, I guess they are kind of close close friends ? if you will.....
I don't want to be in the situation where he is trying to get her whilst talking to me and I start developing feelings, so, how should I approach this without getting hurt ? 
Should I speak up soon ?