Sometime soon, I think I would have a three-person talk: you, your friend, and your partner. I would tell them I am worried about how the competitive element will play into this, but, that I'm willing to give it a try. Find out what thoughts they have if any.
It might be good to schedule a talk such as this once a week, or once a month. During each talk, discuss the status of competition in the friendship and if it is making things bad in the romance area, and what can be done to make that easier. Be honest in saying that you always felt somewhat inferior in your competitions with your friend.
Keep tabs in your own mind of how it's going. What is your emotional state? Is the situation making you a nervous wreck? If so, you may have to step away from it. Unless your partner would honor your wishes to cut ties with the friend, and I'm not sure how you'll feel about that ethically if you can do it.
Hopefully I'm making a mountain of a molehill, and this competition thing won't have any serious effects on your romance with your partner. I just know that I've had a friend, who, for a long time, I wanted his approval, and couldn't seem to get it. That kind of a friendship can be a sad, sad riddle to solve.
Hope this helps,
Love means never having to say, "Put down that meat cleaver!"