Is it normal to become

It's a two way street, don't you think?
Both parties in a marriage need to take responsibility for keeping their romantic lives interesting and exciting. There's absolutely no excuse for not doing so, with all the information available on the web these days, except laziness or lack of interest.
This is a bed you two have made for yourselves; either lie in it as it is, or fix it.

You have become to used to each other. Too familiar. It will take some work but it will also take some talking as to what you each want. It is still there, work on it.

Sex is a wonderful thing that can act as a glue to hold a couple together. As the years go by and they share and weather life's ups and downs together and get to know each other more intimately generally a deeper bond develops that is even stronger than sex. In a healthy marriage as the partners physical appearances decline; wrinkles, hair thinning, growing waistline, etc, hopefully that deeper bond, a profound abiding love and mutual respect will get them through the rest of their life together even if the sex is gone. It's difficult to make the transition from a sexual relationship to a sexless marriage because we don't all get to that stage of our life at the same time, so one partner still wants and needs sex while the other one can't perform or has lost interest. Men are typically at their physical and sexual prime at 22 and it's all downhill from there, losing 2% of their testosterone production per year. Testosterone is what drives our libido. It make us strong and muscular and hairy and horny. A 62 year old man has lost 80% of his sexual drive. The twenty percent remaining seems to be more in the mind than anything else.

I don't know what the solution is for you and your husband. It would be nice if the two of you could sit down and talk about it. Me and my wife have worked our way through it because we have developed a deeper love that's carrying us through, but it's been a little bit of a struggle because we really can't talk about it. I can but my wife can't. She feels uncomfortable with the subject. We both grew up in a time when people didn't openly talk about sex. It wasn't in the media and in the news all the time. Even happy married couples on TV wore pajamas and slept in separate beds, like Ozzie and Harriet, and Ward and June Cleaver.

Maybe you could talk with your Dr about the problem and gain some insight or get some help. It would help if you don't become distant to each other. You both need to feel loved and accepted by your partner even if you can't show it sexually.