Hi I read your post and was most alarmed. This guy is playing with you and you need to get him out of your life.
From my experience, yes obsessive behaviour does go in hand with bipolar. I have been obsessed over many things so that it completely takes over my entire being and makes me nuts.
This is a difficult situation. You are pregnant, but I urge you to break contact with this guy and talk to a Dr, therapist or counsellor quickly.
The only way to stop this is to do it quick and cold. Get rid of numbers, dont answer the phone, or put it down if it is him, refuse to speak, slam your front door on him etc. Or, and this will sound like madness, find something else to obsess about (that sometimes works for me, but I realise this is not good advice).
Sorry if I have gone on a bit, and I am sure others will give much sounder advice than me, but please seek outside help with this, as this man does not have your interests and health at heart. He is bad news. Nannywoofwoof