I have a crush on my girlfriend's mom
Are you being serious? Does your girlfriend know?
Maybe, then I'll try to talk to her about it
You might not want to discuss that with your girlfriend. In my opinion you should keep it to yourself and slowly let the feeling fade away.
Maybe, I just want to see what happens...
You need to let these feelings go away and not pursue them. It would be really hurtful to your girlfriend and would cause an awkward situation for all of you.