Well Mrs. Loss, the presence of a naked man in bed would send most men into a state of flaccid disenchantment! But I don't think your friend's problem lies with his heterosexuality. He sees you as the lover he once had, and hasn't moved on from there; you have (haven't you?). If the situation continues, three relationships will be at risk!
If you and your husband just want a good old fashioned menage a trois to spice up your sex life ... Find someone with no prior relationship to either of you! If, on the other hand, you're desperate to continue with the friend, try adding a little alchohol to the equation... But not too much, or he'll never get it up! - DJ.
A three way marrige can offer voyueristic satisfaction, lesbian sensuality and generally add spice to a sexual relationship. The 'trade-off', however, is there will be three times as many person-to-person conflicts (communication breakdowns, ego pressures, etc). This is why many 'so inclined' couples opt for 'sexual only' participation from the third person. The emotional relationship between the two women can never be the same as the relationship between either woman and the man. Two women have things in common the man cannot share, changing the nature of emotional bonding! Further, you both have a relationship that's been many years in the making. Your new woman will have to start cold ... possibly too much to ask!
While not being a solution to your problem, this may help understanding why any interested women are not breaking down your door. My advice is to look for a sexual-only partner at first, apply no pressure ... and wait & see what develops! If you ever achieve a harmonious 3-way marriage, the rewards will make the wait well worth the effort! - If all else fails, move to Byron Bay!* - DJ.
*Australia's Alternative lifestyle capitol!