This is a really difficult situation and I feel for you. Loving someone who is battling bipolar can be daunting. Not the loving part but having a peaceful life with them part. If you are just dating, this is just a suggestion, but I would strongly evaluate the relationship. Would you be able to have a less chaotic life, more peaceful and stable relationship with someone else?
He's currently unstable it sounds. As in he is cycling and not fully treated. I'm so glad you encouraged him to seek help even though it probably currently feels like that backfired on you. It hasn't. This really will be life for him. He has a difficult road ahead. Hopefully he gets with a doctor (psychiatrist) he likes and relates to and gets solid treatment.
That he is using hook up sites and the tantalizing idea of sex as a release (doing it all day) is pretty common of bipolar. Substance abuse, addiction is common with those suffering mental health issues like bipolar. It's part of the disease and called self medication. This could turn into a substance problem for him as well in the near future or down the road.
If you are a long time girlfriend, you should feel free to tell his family. That he's shut you out after very little treatment, that he seems to be using hookup/porn sites to self soothe and that you really can't help him at this point.
And sadly, you really can't. You did your part and encouraged professional help for him. I hope he dives in.
But sweetie, you DO have to worry about you. His mental health issues are affecting your life and making it unstable. Are you wanting to get back together with him or are you wanting to get him help because you are worried? If you are simply worried, then yes. tell his family. Send an email to his doctor/counselor. I know this is really hard. I again, really feel for you and am here to talk!