It sounds to me like your unconscious is trying to resolve the relationship. There are lots of contradictions in the dream - a good thing happens (you have a beautiful baby) but then a bad thing (your partner leaves). He says he doesn't love you, but throws a surprise party for you. He leaves and has a new girlfriend, but hangs around your place.

Just sounds like your subconscious is working on resolving the relationship but doesn't know how. Does this make sense?