He talks of other women all the time

Is it normal for a guy to constantly look at other women and talk about how he would like to be with them if he is in a relationship? My boyfriend does this all the time and believes it is healthy for us to be honest about how we feel. He thinks we should be able to express our liking for other people and gets upset if I tell him that his behaviour is sexist or that it is bothering me. He says I am not open-minded enough and then asks if I am serious about being with him. I love him, so I agree with him, but I don’t know if I can keep taking this. What should I do? 
No one has the right to tell you how you ought to feel, if something bothers you. Your boyfriend may have his own ideas about what is healthy and what isn’t, and he is entitled to them as long as they do not impinge upon your own beliefs. If his behaviour upsets you, and you think it’s sexist, he cannot brush those concerns away. He can say you’re not open-minded if that makes him feel better, but it doesn’t negate his disrespect towards your feelings. If he wants to be with another woman, you should ask yourself if he values your presence in his life and much as you value his.

I want to break up with my boyfriend but can never do it because he is sweet, kind, and loving. There is just no spark between us, which is why I know this won’t work. I am just afraid of hurting him and making it difficult for him to trust women going forward. How do I deal with this guilt?
Why do you want to live your life by assuming your actions will change how he engages with women? It is presumptuous and ultimately harmful to you both, because you are with him for the wrong reasons. If he is sweet and kind, he deserves honesty.