Only a very small part of the ejaculate is made of sperm; the rest is what would be called "inactive ingredients" if your husband were ejacuutf8g, say, toothpaste instead of semen. The carrier fluid coagulates briefly, just so it won't run down your leg before the sperm have made their escape. Once the sperm have gone, the leftover gunk liquefies and runs down your aforementioned leg to form the "wet spot" of lore. If it didn't, you'd be carrying the leftover goo from a lifetime of sexual encounters around with you until you scrubbed it out with a bottle brush, and that is not a nice picture.
You're fine. If your question really does reflect your general state of knowledge about these things, please get a book. Get several. Get a library card. This baby-having business is not simple, and while there is such a thing as too much information, too little information is worse.
Andrea's on vacation this week; this column ran previously (12/12/06). But she's still checking e-mail and eagerly awaiting your questions about love and lust!