I'm sorry your hurting.
This is a really new relationship to be honest.... 4 months isn't all that long. This should still be in the " honeymoon stage"
When you add Bipolar into the mix and your trying to find your footing and the searching for the right meds and working hard in therapy.. Having a relationship Bipolar or not can be hard and difficult at times.
I have Bipolar.. So I will say it takes time and work to figure how to have a life with Bipolar in it . Yes it's possible. I think you need to do the work an find stability , then a relationship might go more smoothly .
If he's voicing that maybe he just doesn't want to get further involved with you , then listen to him .
Be kind to yourself