I have, numerous times. I have social anxiety disorder, so I keep telling myself that I am not good enough for them and they deserve real and better love from someone else. I just crush on these guys from afar, I never make a move or try to talk to them. I feel like I fear that I might hurt them, sort of like elsa from frozen. I just fantasized about being with them or even being their friend. It is a disorder, so I don't feel too bad about it. I just go with it.
I have issues with codependency and dated a woman for two-and-a-half years who I now believe struggles with Borderline Personality Disorder. So, in a sense, yes, I have been infatuated with someone. Because love should be a two-way street of self-sacrifice. When it's only one-way, that's when it's infatuation.
For the pain and regrets of that relationship, I'm thankful for having went through it. Because I refused to lay all the blame at my partner's feet and sought to understand what my contribution to our downfall was. Then I found out what Borderline was and also understood my role as a codependent in that relationship. Now, armed with knowledge of my own issues that were invisible because they were my "normal," I'm on the path towards healing and recovery. I'm becoming increasingly ready for a healthy relationship and looking forward to it. :)