I think the replies so far have overlooked some critical considerations in evaluating your situation, Casino. I suspect it is likely that your relationship with your best friend is interfering with your love life.
First, is your best male friend a former lover? If so, I think it's understandable that your prospective boyfriends could find this rather cowing. The idea of a former lover being involved in a current relationship as a "consultant" is inadvisable for what I hope are obvious reasons.
In any case, the main factor, I think, is the priority you award the relationships in your life. If your priority is to have a best friend, be that female or male, then that potentiates a particular result. If your priority is to find a life-mate or a serious romantic relationship, then that will also incline one toward certain consequences. This isn't to say that it's "either-or"; the point is simply to be aware of what means the most to you in your life.
If your highest relationship value is a serious romantic relationship, then you should prioritize accordingly. Situations which will tend to negate your chances of finding and maintaining such a relationship ought to be examined with an eye toward minimizing their negative influence. For example, you would plan to spend more time with your potential love over that spent with others. You might give up your traditional Saturday outing with your best friend or your daily book club meetings, for the time being.
In your case, Casino - assuming you're serious about a romantic relationship - I would suggest that you devote the lion's share of your time to your budding relationship during its formative stages, and make it abundantly clear to your prospective love that he is your first priority. If and when you tell your potential love about your male best friend, make sure that he knows that neither he nor others will take away from time that you would otherwise spend together. Of course you would want to spend some time with others, but the point is that your *first* priority will be him (barring medical emergencies or the like

).
In this scenario, your potential S.O. ought to feel reassured and secure in his status, and from that strong position would likely be more accepting of your male friend.
Inevitably, if your relationship grows, your new love will become your best friend and lover, and your former best male friend, if he is indeed a true friend, will honor that and gracefully accept his "demotion."