Need help with my wife...not attracted to her, or her attitude.?

I've been with my wife for 7 years ( my second marriage, her first ) and married for almost 4 years. We have a wonderful 2 year old boy who I would do anything for. After my wife got pregnant our relationship started tanking. She was always spirited and speaks her mind which I love, but it started turning into a bash fest on me. Every fight we've ever had is because she starts spouting off without any regard to me. About 90 % of the time I can take it, but I'm starting to lose it. Fast forward 2 years now...my wife has always been thick and that's a good thing in my book, but she gained a lot of weight, no longer dresses to attract me, wears old lady night gowns to bed, etc. I'm no saint and I'm not perfect but I've done well to maintain myself over the years. I try to always look good for her. Now she's starting to lose weight and is looking better, and is working on her attitude, but it feels too little too late as I am no longer attracted to her. I have no feelings when we kiss or if she touches me...I hate it because i want to feel that way towards her again. Unfortunately I met someone else and although I feel very strongly for this person, as the cliche goes, I broke it off to work on my relationship...I'm now at my wits end and i want to be happy, but I have no idea what to do next. We've talked and are both willing to work on our problems, but I will not tell her Im no longer attracted to her, or that I'd rather be with that other person at this time...help!