I think it's true that you will never *forget* your first love, but there's no reason in the world that you can't love another person more!
I only had one serious relationship before I met my hubby. I was friends with my ex for a while before we started dating, and then we dated for about a year in college. Like most people with their first love (I think) I felt "head over heels" ... Even though we were young (18-19) and didn't discuss marriage, I "knew" we'd stay together forever, get married after college, etc, etc... However that obviously didn't happen
During the last few months of our relationship I began to realize that we weren't as compatible as I thought we were, but I ignored all the warning signs until he broke up with me. It was a friendly breakup but it was still devastating to me -- and it didn't help that I had neglected to form any close friendships while we were dating, I thought he was all I needed. So I felt very much alone. We tried to be friends afterwards, but for about a year after the breakup it really took a toll on my emotions, because every time we were together I was just reminded of my feelings for him....
But I eventually got over it. I started making more friends in college, and going far away for a summer internship and making new friends there really boosted my self-confidence and completed the healing process for me. (Even my roommate said she noticed a difference in my self-confidence and maturity when I got back from that internship!) For my last year in college I actually enjoyed being single, and had a great time with some of my friends -- and on the rare occasions I did talk to my ex, I didn't want to get back together anymore. I was finally happy with who I was, and didn't feel that I needed him to be complete or happy.
So when I met my hubby right after I graduated and we started dating, I knew that I was dating him because I liked him, not because I was desparate or lonely! (In fact, I met him the summer between college and graduate school, and I had planned on being single all through grad school, thinking I would be too busy studying for relationships! So he took me by surprise!
) And now, I don't miss my first love at all -- I can now see that hubby and I are a much better couple than my ex and I ever were. Even though I still think my ex is a very nice, wonderful guy, our personalities just didn't "click" like hubby and I. I always had a hard time figuring out what my ex was thinking or where he was coming from, but with hubby, it's very easy for us to understand each other!
My ex and I still talk on occasion (like one email every 6 months or something), because I do consider him a friend, though not a close friend. So I guess yes, I have stopped loving him in a romantic way, though I still care about him as a friend and hope he's happy in life! (And I think he is, he just got married and his wife is a much better match for him than I ever was!)
Sorry that is so long, but I think each person is going to have a slightly different answer to your questions based on their experiences!