9 month old border collie terrified of life

[Boaty]

I recently moved 3500km across Canada. I've had my pup since he was 6 weeks old, he used to be very good around people, and very affectionate. He was out running with cows all the time, and just loved life. Now we live on the edge of town and he is scared of everything outside the house, and attacks the broom/vacuum, he's very reactive towards other people and dogs outside of the house. But very affectionate isnide. I take him out 3-4 times a day on walks and always try to let him run for at least 2 hours a day at a park close by. The only thing that I can say is very different is my roommates have a dachshund that is very aggressive towards him. He gets along with their pug but not at all with the dachshund. He will attack my pup for even just walking close to him. Would that cause him to be fearful and reactive? My BC isn't fixed and both of the other dogs are. And I feel like my BC let's the dachshund be the alpha cause I've seen him go up against a 2000lbs bull when he was 6 months and there's no way a 25lbs Weiner dog is gonna be a bigger challenge to him. It's quite confusing for me. I've been around dogs my whole life but this is the first one I've had myself.