Need some advice

Last year I met and dated a guy for about 5 months. I was falling in love with him but he got scared and said he wasn't ready for a committment. At the same time an ex-girlfriend also became sick with cancer and suddenly wanted him back. He said he wasn't sure what he wanted so I walked away. This past fall we started talking again and started a FWB situation. Well needless to say we continued to get closer and I feel for him again. I've just found out he's continued to visit his ex. Now that I've found out he admits he wants a real relationship with me but also wants me to accept him standing by his "friend" while she is dying. We're both divorced with school age/teenage children. His ex causes significant problems in his life which I am completely accepting of dealing with and being there to support him. But an ex-girlfriend is too much for me. I feel extremly hurt and think he should walk away from her if he really wants a relationship with me. What do others think?