srsly this is just reality. today is only one day. there will be more. just chill out. other parts of your life don't get put on pause just because OMG we haz teh poly relat'nshp OMG. what would you think it would be like ANYWAY with a baby and one on the way.. I don't even HAVE kids and even I can see that.
OTOH, if your partner is ignoring you and treating you like you're in the way but has sexy-time with the other one that's not cool either. But look within yourself. the answers are already there.