Find a bisexual woman who can love both of you. OK, just kidding, sort of. But sometimes when there are no easy solutions you have to consider "out of the box" thinking.
I've been in a similar situation myself, where every possible solution is either one that won't work, or one I don't want to consider.
In a situation where you don't think you should have to lose your friendship due to the sex... It may be an amicable work around.