What's your opinion on dating someone, even though you have feelings for someone else?

I ask this because I have this really close guy friend who started dating someone a month or two ago, but he has strong feelings for me. I addressed it with him a few weeks ago, and asked how he felt about me (to see if he still felt the same as he did before), and he said that he still feels the same way. We talked about it for a bit and he even said things about how he would marry me in a heartbeat, because it's what he's always wanted. We've discussed this before, but decided that waiting a little bit before starting a relationship would be best (I won't get into that), so I was baffled when he suddenly got a gf out of the blue. Well, we are going to get together soon to have a serious discussion about this whole situation, but I feel bad talking about this because I know he has a gf, and if I were her, I would be so upset to know my bf has such strong feelings for another, and is talking about being with her forever and such.





So basically, I'm just curious what people's views are about being in a relationship with someone, even though you have strong feelings for someone else? I know he's not cheating or anything, but I know if I were in his place, I would feel so guilty...What's your opinion on dating someone, even though you have feelings for someone else?
i was in the exact same spot. i ended up acting distant, getting dumped (which i planned to happen) and now im free. free to go get that other gal thats been on my mind for so long.