Cheshire has an amazing post called "Sex with Crazies" that I think any person with disabilities should check out. As someone who is determined to live unashamed of being quite mad, I simply adore this post. It feels like she dug around in my head and picked out exactly how I feel about this.
Sex allows me to physically connect with my partner, who is the only person whose judgment of reality I know I can trust more than my own. Sex makes him real to me and it makes me real to myself. It's a source of certainty in a world where I'm sometimes not quite sure about a lot of things. In essence, it is something I need.