I was working for a big company and I felt bad about the work I was doing. A friend (let's call him Tony) from my school (I am recently graduated) offered me a good position in his company. He does not own the company but is working hard here and is well respected. I accepted and I'm currently working there and I am very happy. On top of this I got back in touch with an old friend of mine (a girl, let's call her Sara) and introduced her to Tony. It appeared that Sara's best-friend (let's call her Alice) is the ex-girlfriend of Tony, and now we formed a friendly group of four which I really enjoy. The relationship between Tony and Alice is set, neither of them want more than friendship.
We hang out 1-3 times a week at night, because we all work during the day, and have a great time chilling outside, dancing and chatting. From the first time I saw Alice, I had strong guts feeling for her (she looks very attractive to me, and she is a very kind person, she loves animals and me too). At first I locked this feeling away and said, it's the ex of my friend I just can't let myself feel that for her. And everything was OK, the feeling was here but I was able to ignore it. But since the last 3-4 times we hung out, she started flirting with me in a very polite manner, full of compliments and really nice eye contact. I just can't handle the feeling right now and I'm really thinking about dating her, but I feel really bad about my friend Tony and I don't know how he'll react.
How can I explain to Tony that I want to date his ex? I know I have to follow my feelings, but I'm really scared about failing the new relationship and destroying the group of friends we have now... I really want to know more about Alice, but I want to keep this group up. Any advice is greatly appreciated.