"I hope this isn't a stupid question, but can men with Asperger's or HFA have normal intimate relationships? I want to know because I'm currently dating one and I'm wondering how far to let this relationship develop."
That would depend on one's definition of "normal." What's normal for one couple may be quite abnormal to another. In any event, it is very possible for men and women with Asperger's and High-Functioning Autism to develop an intimate relationship WITH THE RIGHT PERSON (i.e., someone who will learn about the disorder and make any necessary adjustments in relating to the Asperger's partner). In some cases, that “right person” may be another individual with the same disorder who understands and has the ability to cope with the idiosyncrasies of another person on the autism spectrum.
Some of the barriers to relationships include a sort of “extended adolescence” or maturity issue in adults with Asperger's. This can mean that the individual marries later in life and lacks the ability to have solid relationships until they are older.
One of my Asperger's clients recently stated that he feels that the relationship with his wife is challenging, in part due to his overwhelming need to focus on his obsession of choice. He feels that he lacks a strong interpersonal connection and has to make a conscious choice to put his focus on his wife, to the exclusion of his desired focus of choice. He is accustomed to being solitary, and he finds it difficult to concentrate with others around him, including his wife.
Relationships do take a lot of work when one partner is on the spectrum. The social skills required make relationships challenging for adults with Asperger's, particularly if diagnosed with it in adulthood. Unfortunately, the divorce rate among couples affected by Asperger's (i.e., one partner is on the spectrum, and the other is not) is higher than in other groups of people. However, interventions (e.g., marital counseling) can work well if the therapist understands the unique features of Asperger's as it affects relationships.
We don't know statistically how many Asperger's men develop "normal" relationships or how many find themselves unable to relate to a partner in an interpersonal and intimate way, but we do know that those with good communication and social skills have a better chance to succeed in a relationship than others.