My wife also gained tons of weight after having children. She was as big as a whale. Yes, I admit that I was sad when I noticed that she was not loosing that weight afterwards. Where was that sexy chick? Gone. But we still had sex. I did not have to focus on what she did not have. I know what she can look like, and I love that, not her temporary situation. Later, probably because I was never bothered by her weight, she decided to watch her foods and slowly lost all of that "baby fat". Now she looks great.
Possibly the best way for you to deal with this is to do family therapy. I recommend "Transactional analysis" ("TA"); you should be able to find some therapist who knows "TA" in your area, but be careful, a good therapist is hard to find. If you don't like a therapist, move on. They have to be genuinely interested in you and share most of your values.
I personally would not be surprised if your husband starts cheating on you. But look at him as a spoiled little child: he is bound to do all kinds of stupid things until he grows up. Therapy is the best way. If he refuses that, then he will probably learn through harsh experiences in life.
I would not worry about whether your husband is sexually attracted to you. Attraction comes from brain, not from eyes. I know many incredibly sexy looking women who I would never want to touch because of their personality. That's why I am with my wife. Looks help, but don't go very far. I don't think your husband is gay either. He is just spoiled and selfish. You need to start loving yourself. The more you work on yourself, being more introspective, the more you will appreciate yourself. Instead of focusing on your husband, try to see what you can do about yourself (your looks are least important).
BTW, I would ask my husband for a serious talk. Tell him that you don't like where your marriage is going. If he brings up your looks, ask him if he did not know that women gain weight during pregnancy; if he compares you to someone else, tell him that you are now talking about you two - he did not marry someone else, just like you did not marry Brad Pitt. Then bring up all those things that bother you: that he is showing lack of respect by suggesting that you are cheating; that he is showing lack of interest in you; that he is (probably) not helping you much around the house; that he is not the same loving guy you met and so on. If he says the same about you, you will know he is not interested in the conversation, only in arguing. You can remind him that you are trying to have a nice conversation with him, not an argument.
I wish you good luck and never to loose that loving, good part of you, even when people around you think that they should take advantage of you. Just learn to give only to those who also give back.