Well it all depends on many factors such as; How long have you guys been together?, How long a go was this ex been out of his life, was it his first love. There are a number of reasons why he may or may not have feelings for her. The best way for you to honestly find out is confront him about his connectedness toward you, tell him that you are not so sure that he is all there to support and help you through all the things that you need in a relationship. You could also ask him flat out if he dose if he says no then take his word for it unless you have proof other wise. This is not an uncommon feeling my girl friend confronted me about these thing a few months after we where dating and come to find out I wasn't until we had the talk so thats all you guys need is to talk about these things.
It can depend. Like does he act different around you when she's there
Does he talk about her? Does he speak her name when you are making love? Hope this helps!