Is it normal to feel this way about crushes?

Over the last few years, i've had various crushes on people and i'm worried that i take my infatuation too far. When i have a crush on someone, i then imagine what it's like to be in a relationship with them and I think what it would be like if they were with me at that moment. This also applies to when i go to sleep at night: I lay in my bed and imagine that they are laying next to me and i depict a conversation with them in my head. Not all of these crushes are people i actually know; sometimes they're strangers that i found myself attracted to and if i find out that they have boyfriends, my heart sinks even though i know i have no chance with them. I'm getting really worried that this is affecting my mental state and i just wanted to get some opinions on this. Is this a normal thing to feel?