'I don't enjoy having sex with my husband'

Is it okay to tell my husband that I don't like having sex with him as often as he would like to? I don't enjoy it, but he gets upset whenever I talk about it.
If it's not consensual sex, it's a problem. You are entitled to your opinion and your body belongs to you alone. Try finding out what doesn't excite you though, and try fixing that. Speak to a professional.

I am a 42-year-old married man with no children. My wife and I have drifted apart over the past 10 years or so and no longer speak to each other much, even though we live in the same house. We are comfortable with this arrangement, where we are more like roommates than a married couple, but I sometimes feel as if I am missing out on the joys that come from being married in the true sense of the term. I get no companionship, which is what I thought the point of marriage was. I am considering a divorce, but am nervous about doing this at such a late stage of my life. What do you suggest?
Living like strangers for a decade is tragic, in my opinion, simply because you have just one life and it's sad that you must go through it without connecting with your spouse. This is tragic for your wife too, despite the fact that, as you say, she appears to be okay with it. Why not tell her how you feel and get her to understand that there must be more to life than this?
If she agrees with you, it may change the way you both live. If she doesn't, it may free you both to get on with your lives and possibly find some measure of happiness elsewhere, even if you both end up alone. As for being nervous, age is just a number. I urge you to look at the life and times of a certain musician called Mick Jagger for inspiration.
Good luck.