I completely understand your feelings, and Drakes. We just went through the same situation. I will tell you that it will change your relationship with Drake, which was one of my concerns too. Chester and I are VERY bonded, and I am still a bit worried about giving Mille enough attention and still making Chester feel loved as much as before. It was a very hard decision for us. Chester has also had issues with other dogs (fear agression) and I was also worried about the new dog coming in and taking over and dominating Chester. Fortunately, it's all working out pretty well. We've been to a behavoirist and are working out everyone's issues.
Probably a female would be the best companion for Drake. He would most likely feel less territorial.
I must admit I resented Millie a bit the first couple of weeks and I was very suprised by those feelings. Chester was more interested in being around, playing with, and generally checking her out, more than being with me. But things are settling down now and we're getting back more to our old routine. And boy do they have fun together!
I guess what I'm trying to say is it really is worth it. I wondered there for a bit, but now its great!
We thought this out for about a year, knowing what an important decision it was so take your time.
Good luck with what ever you decide, and I hope this helps.