I am having anxiety about my feelings in my relationship

I am having anxiety in my relationship with my girlfriend. Few weeks ago I woke up in the morning next to my girlfriend and everything was fine and I kissed her and said I love her before leaving for school. When I got to school there was this girl looking at me and i looked back. When I got into the classroom I started to wonder ehat if I don't feel those feelings for my girlfriend. It's like these thoughts have been trying to interfere with my life in these few weeks because I am 100% sure that I love my girlfriend and that I want to spend my life with her. I can even see a future with her. Nowdays most of those thoughts are " I know that I love her and that I dont want to leave her but should I break up" those thoughts really are pretty scary because why I can think like this even though I know that it isn't true.

I do have a tendendcy to overthink and get anxious about little things and then those thoughts will always snowball. I have told my girlfriend about these and she has been really supportive and wants to help me in anyway that she can. My psychologist told me that I may have anxiety disorder because these thoughts are unwanted. And I am scared that now when I think about these so much then I will really lose my feelings.

Only question that I have left is that are these thoughts true or false made up by my anxiety disorder.