I just need to mention that "intimacy" is not the same thing as "sex."
Is it "sex" that you need, or "intimacy?"
Every romantic relationship needs intimacy. That can take many forms: cuddling, eating cake together and smearing icing on his nose, interlocking arms while you walk from the car to the grocery store, holding hands while you watch tv, sitting down and talking about your feelings...
You can't meet your relationship's "intimacy needs" from a person outside your relationship. They must be met between you and your husband.
Now, all of that is 100% separate for your sexual needs. If you need sex and your husband does not, then that is something you can meet outside the relationship. Just make sure you're clear on the distinction.
I'm in a rather asexual stage right now, I go through them from time to time. If my husband came home and said "I need intimacy, I'm going to go have sex with someone else" then I would feel rejected. I believe that we have a very intimate relationship; I make a point of doing my part in being intimate. But if he came home and said "I'm really horny. Do you want to have sex? No? Do you mind if I go have sex with someone else?" then I would encourage him.
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker