I have two dogs and the second came home right before my first's 1 year birthday. It has been 9 months since #2 came home (Ella Bean - my lovely Yorkie mix!!). It took about 2 months before they started playing together, about 4 months before they started snuggling and cuddling each other and now, they are inseperable.
Walking them together for about 30 minutes a day really helped bond us as a pack and helped Louis accept Ella.
At first, my dog Louis, who was with me first became territorial and protective of me, his space and toys and now he shares everything. It took patience and giving the first dog lots of treats whenever the 2nd dog was around, so Louis associated Ella with treats and feeling happy!
Be patient! Good luck!