It depends. Let's say the character (or you) "used to think romantic love was a neurosis shared by two" until something happened last week.
Today, someone asks him/her/you "what did you think about romantic love yesterday?" You should say:
I used to think...I no longer thought that.
You're talking about what the character/you thought yesterday, which is in the past, so past tense should be used.
But if someone asks "what do you think about romantic love?" they are asking about the character's, or your thoughts right now. You should use present tense here:
I used to think...I no longer think that.
Again, it really depends on whether you're talking about the character's/your thoughts at the time of writing or before that.
A couple of examples that I wrote:
- When I was little, I used to think there was a monster under my bed. By the time I was 8 years old, I no longer thought that.
Here, I'm using past tense because I'm talking about what I thought when I was 8.
- I used to think vegetables were the most disgusting things in the world. Now, I no longer think that, and I do eat them, but I still don't love their taste.
Here, I'm using present tense because I'm talking about what I think right now.