I [25/F] am beginning to identify relationship pattern I have that is worrying me

I'm not sure this is the place to ask this but I thought it wouldn't hurt to ask.

It usually starts off when I meet a guy who I am attracted to. I tend to view them with rose tinted glasses, I think they are perfect and I feel ready to settle down in a relationship with them.

Then I start losing interest. I start noticing flaws and things that I don't think I can deal with in a relationship with them. They annoy me. This is all relatively normal until my lack of interest starts turning into disgust. Their appearance, flaws, everything about them starts to disgust me. At this point, if I hang out with them, which I often do (I understand that it's best to just let them know) because I have a hard time saying no, I will feel physically and psychologically sick in their presence.

I guess I want to know, how on earth can I go from being so enamoured by someone to absolute disgust? Is this normal? How can I predict when this is going to happen? I feel so bad for "leading" them on, but I'm not really leading them on as I initially felt a real attraction to them. How do I stop this pattern?

tl;dr: I lose interest in relationships unexpectedly and want to know if this is normal