NEED BEHAVIOR HELP ASAP

We adopted Patches in May of this year without much knowledge of his life prior to the shelter, except he does not do well with cats. He is a neutered male I will stated here. When we brought him home he was great, the only concern was his leash pulling. He was introduced the next day to my parents three females labs and seemed a little timid/scared at the first meeting but since they have become the best of friends, especially Patches and the yellow lab Summer. When we would take him for daily walks at our apartment (3-4 times a day) at least 2 miles a day, he did not pay attention other dogs at all. He then met another male dog and was much more energetic and would hump the other dog when they saw each other. Another night he came across a mix breed dog who was very aggressive and working with a trainer outside. When the trainer approached the other dog snarled and lunged at Patches, Patches did nothing but cower a little. Now we are in a new apartment complex and Patches has progressively been getting worse and worse with his aggression towards other dogs. The past month or two we have been actively working on leash training him, his pulling has gotten better but is not consistent and also he understands sit pretty well indoors but is very distracted when we are outdoors. His walks are enjoyable as long as any sight of another dog or deer is near. The second another dog walks by us or is in our view he begins to pull and whine, he has even begun barking very aggressively with snarls mixed and lunges at the other dogs, does not listen at all when he is told to sit or he is pulled in the direction of the walk we were on. He resists forcefully being sat down by myself or my boyfriend. He is a big boy, at about 75 pounds and pure muscle. Our worst fear and encounter took place this evening on our routine walk back from to our apartment from the complex dog park. A smaller mixed breed female dog and her owned came walking down the stairs. When we saw them we forced Patches to sit, he then resisted began jumping and snarling so much and lunging that he was able to make me fall over and get lose his leash from my wrist.. He attacked the other dog. No blood was shed and thankfully the owner is not pressing charges or anything. We have a very real and big problem. Is this territorial? We think we have made him into the aggressive dog he has become? Could our energy be what he is completely feeding off of when he gets like this? Please help us save Patches life.

1
Mapping: DefaultPageMap
Map Field: TopLeft
Ad Slot: PW1_RON_Top_Left
Size Mappings: Desktop Only
Mapping: DefaultPageMap
Map Field: TopRight
Ad Slot: PW1_RON_Top_Right
Size Mappings: Top_Right
Submit your own photos!
Dog Breeds Selector

Find your perfect match based on activity level, size, intelligence and more!

Mapping: DefaultPageMap
Map Field: BottomRight
Ad Slot: PW1_RON_Btm_Right
Size Mappings: Btm_Right