This sentence is worded kind of oddly without seeing its context. However it seems that the speaker is speaking about their thought/feeling in the past specifically. As in, “When I was younger and my sister got in trouble, sometimes I would think that maybe it was my fault” This sentence specifically though implies that you used to think it was your fault, while leaving open the possibility that you may still think something is your fault. However, from this sentence alone and the use of “would,” you can’t infer that the speaker still believes that it’s their fault in the present, but it’s possible. If that makes sense. I hope this helps!

Thanks a lot for helping, Miles. It's helped, thank you for complete explanation!

Yes. It means that, in the past, you often thought that.