He certainly can have feelings for you both. It is possible to love two individuals at the same time but in different ways. He probably wasn't planning on getting involved with you but it happened and it sounds like he wanted to make sure you were genuine. He has had time to find that out about you and vice versa. It is not just him that is failing to make a decision. You are also hesitating because you fear loosing him.
If he chooses to stay with the other girl then actually you never had him. Presently, you both sound like you are violateing your own personal codes of conduct. This will only lead to disrespect for yourselves. It will also become easier as time goes on to vindicate the cheating and will become a source of mistrust between the two of you. By this I mean, that if you stay together whether the other woman is in the picture or not, you will begin to wonder if you both could cheat on one another as you are now. Frankly, it is a bad precidence to set, as it can become something that is easier to do each subsequent time. Beware straining your moral bounds.
To answer your question, the only way he is going to decide is for you to tell him that your conscience is bothering you about how the two are conducting yourselves. Explain, that you care deeply but that you cannot continue to sneak around and cheat with him any more. Tell him that you have too much respect for him and yourself to put the two of you in this situation. You can explain that you are ready and willing to make a committment the moment he is a free and single man but until then you are going to make the decision to stop seeing him.
This is the only way you will ever know if he really wants you and only you. It is also the only way you will prevent yourself from creating a cheating partner as you go into the future, whatever it holds.
