As a designer who does both print and web I have found that I can design and develop relatively straight forward web site on my own. I have taught myself HTML and some JavaScript and have found it very satisfying in a different way than print. You just have to realize that a web site is never really “done” it is always changing. Which can be a nice revenue stream if it doesn’t drive you crazy. :)
For larger project such as mobile app and web sites that are database driven I have found the need to partner with a developer who can write the code to support my design. I’m sure that there are those who very good at both, but learning how to program is a whole level of difficulty beyond HTML and CSS.
The good news is that if you own the Adobe Suite you may already own Dreamweaver and that will be a good foundation to start learning on.
I love print and interface design, they’re constraints and compromises are different and that keeps it interesting, those times when I’ve just done one or the other I got board.
Hope this helps. :)