u/BeerInsurance

The wall beneath my dining room window started to bulge pretty badly within the last few months. It got to the point where I was easily able to break into some of the plaster and I can see evidence of water damage. The second photo is the opposite side of the wall on the exterior. If I seal this spot with mortar, will that solve my problem? It’s a large section and I’m going to have to patch with drywall as opposed to plaster, but I’m wondering if the lathe is fine to leave as is or will my drywall just be a bandaid to a bigger problem…? Any advice is appreciated!!