Sounds to me that you're depressed because you're not getting enough attention from her. This is a common situation for single people dating divorced/single parents.

Basically; she's got to juggle her life with her dependent, which is her kid. Therefore; she is thus unable to spend as much time as you would like with you. Because you can obviously take care of yourself (as you're an adult) as compared to the kid. This is the exact same situation that spouses (whom have been pampered by their other half) go through when a new kid arrives and that the spouse is no longer the top priority.

This is something that you'll need to understand/accept. She WILL prioritize her kid above you. Because the kid has no one else, unfortunately. If you're REALLY serious about the relationship; rather than taking it personally and being depressed, why don't you try to spend more time with BOTH her and the kid? Try helping out with the kid as well to take your mind off the depression. Kids can be excellent stress relievers and this will also help with the relationship.

All I can say is that dating a single parent is waay more complicated as you basically have to be the 2nd half of a married family. Only you can decide if this is something you'll be comfortable with.