I'm in love with a married guy. He claims he loves me but it doesn't show.
Unless you have an open conversation about polygamy, it will end in tears. Make him man up! Insist that you want a commitment before he gets any more access to your time or your body. You also have to take responsibility, because you know that's another woman's husband. If you are okay with being a second wife and he is man enough to introduce you to his wife and the three of you reach an agreement, all will be good. If not, get your own man.
If your intuitions tell you so, just leave him. Be happy