I have always been mono when it comes to sex in a relationship, if it isn't happening at all at this point you need to ask questions. It might be the NRE with her partner is leaving nothing for you. Also it could be that she is trying to end things like RP said. Also Also, you might want to ask what her preference is about multiple guys in the same day. I know my gf doesn't want to sleep with both guys in the same day. So if the OSO is getting it that day it is not going to happen for me
. Talk with her and figure things out. There are so many things it could be. My ex and I fell out of sync after 16 months together, by the 20 month we were over. I asked and asked she just said that she wasn't horny, I knew our connection was over.