My wife is gaining weight

Before I start, I want to say that I really love my wife and I am posting on here to see get some advice. My wife has always been on the heavier side. We got married about a year ago and she had me convinced that after getting married we will support each other in keeping an active healthy life style and motivate each other to go to the gym and eat healthy. That never happened after we got married. She always was stressed, did not feel well or had too much to go to the gym. Now she is pregnant with our first child. She has found this as an excuse for her gaining weight (she has but she was already about 50 pounds over weight). I love her to death but its come to a point, I am not attracted to her sexually. I hate saying this but I cannot help how I feel. Frequency in sex has gone down, I hardly initiate sex. Its been about ten days since we were intimate, I have no desire to be with her. I really feel like a douche bag. I cuddle with her, hug her, kiss her but I dont want more. She has started to note this too. I have tried to be politely mention that I know she is pregnant and cannot work out but she can still eat healthy and walk on the tread mill. And she goes but that becomes into an excuse to eat stuff like Angus Burger at McDonald's and that really ticks me. This becomes into a fight. I know she has cravings but a 1000 calorie milk shake is going to do her more harm than good. The other day she wanted to go to the gym, changed her mind, dropped me off and had a meal at McDonald's. I do not know how to approach this situation. She is pregnant and i love her and want her to have a great pregnancy but this is really causing problems. I do not know what to do... Any advice would greatly be appreciated...

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