I also had a mastectomy and only have one breast. I am not going to get a breast implant because I don't want the complications that go with it. I bought a breast form for a little over $300 at Nordstrom. It's made of silicone and you insert it into a pocket that is sewn into a bra. Nordstrom has the special bras with the pocket but they will also sew this pocket/s into any of their bras. When I found the right bra and breast form I found that I could wear ALL of my clothing, even the tighter tops without anyone knowing that I only have one real breast.
As for dating--I totally understand your embarrassment. But maybe it's a good test to find a guy that is going to stick by you through thick and thin. If a guy can't handle it--do you really want this guy in the long run? At least he still can see your one lovely breast. Embrace the fact that you still have one breast and you are alive and well.
I live with this problem of not accepting myself because of the loss of my breast. I know it isn't easy, but you have to remember how lucky you are that the cancer is gone. Consider the fact that you could have lost a part of your body that was more functional--like an arm or a leg or even a hand. Your breast didn't serve a super important purpose. Millions of women live with mastectomies and have the breast forms--not the implant--and live good happy useful lives.
I wish you all the luck in the world. Just try to be strong and positive whenever you can.