These feelings have come about because you are having problems in your marriage and this man has shown an interest. They are confusing but quite superficial and if you cut contact you may be surprised just how quickly these 'feelings' disappear.
He is showing big red flags and it would be best not to get involved with him at all. Concentrate on your marriage, if you can fix it then all good, if you cant you can go your separate ways. But do so on your own, this man is not going to solve any problems, he will only create them. He has you questioning your sanity now, imagine how you would feel if you were actually in a relationship with him. Sort your marriage situation out and if you end up single, thats no bad thing. You don't need this man waiting in the wings.
Frankly, he sounds like trouble, checking up on you is not good at all and you say yourself he is manipulative. You are not mad, you are confused and this man knows it and is seeking to take advantage. Get him out of the picture and you may find things between you and DH improve. Its hard to think clearly when you have a demon on your shoulder. Concentrate on yourself and forget about anyone else.
And don't tell him where you are going the next time you go out with your sister, he has no right to check up on you, i would be getting angry about that, not confused!!!
Im sure you will get some better advice soon but i know how you feel with one relationship gone stale and another man trying to confuse things. Please for your own sake forget about him. Its hard but try and stay strong, good luck