If the nice guy is serious about starting a long term relationship with you when the time is right ( is he, and you absolutely sure him & his ex wont get back together?) Then I would probably have a chat with him & say look, my time is running out, how do you feel about a one night stand sort of situation to help you fall pg. Or as suggested, a home insemination kit. I don't think I would take up your other male friends offer as lovely as that is of him but it sounds like its just adding to a complicated situation.