It sounds that you need to get out of her house and date him in a hotel, possably with dinner or a movie first if you can afford that, or you can order pizza and watch a film on tv/laptop. Going for a stroll together is also free. There are lots of sites that suggest fun things for couples to do, sex being one of them
Also, since she is your friend and you want to continue to see her, I suggest that you can invite them over for dinner at your house, or at their house if you get a sitter/if your kids are old enough to look after themselves at dinner time.
Polyamory and scedueling time go hand in hand. I KNOW it is temping to just go with the flow, but that is not workable when you have several people and work and all the rest. Sure some things may unfold naturally, but you have to have some kind of basic rules to go by, so that people know what to expect and so that time is not eaten away by stressors. Your boyfriend should also plan active "dating time" with his wife, even if she has nights with him, because "special time" together is different than maybe a quickie and a kiss before going to sleep. She too needs to be dating him. I don't really se how your husband enters the picture, if he is working away a lot I don't see how he can keep any relationship, apart from the one with you, going. Are you all on Skype? Is he available on phone? If he is going to pursue a working LDR, that will take time and effort to be strong between visits.