i want to let you know that it is ok to love a lot of people, and never, ever become romantically involved with them. As sexual beings, it's not unusual to have sexual feelings about any number of people (friends or strangers, perhaps even "enemies"), but knowing when it is appropriate to act on them and when it isn't is the real art of being a sexually responsible human being.
So, i say that it's ok to love other people--particularly your "best friend"--and ultimately love and have a sexual relationship with a person who wants to have a responsible, loving sexual relationship with you.
for example, i am married to a wonderful man. He's the only man that i've ever had sex with, and unless he dies young or before me, or i divorce him or something silly, it's likely that he'll be my only partner. But, i also have a lot of male friends whom i love very deeply. Some even i'm greatly attracted to. Most of them know that i love them because i tell them that i love them. Some of them know that i have sexual feelings for them as well, because we've mentioned it. My husband knows about everything. Since we're all adults, we all value our relationships (both sexual/marital and otherwise) and won't do anything stupid. We rely on each other in many other ways, care for each other deeply, and spend a good deal of time together.
But, it's all open and healthy. The love is starting to suprass romantic notions and become a real community of support. we can't help it that we're all just loyal and passionate. BTW, my husband has also told many of these men (as well as other women in our community) that he loves them, although he doesn't have sexual feelings for most of them. We are all very affectionate though.
Anyway, perhaps this helps? and perhaps you should/could talk to your friend abotu these things.