Since there are two separate issues here that are bothering you I will address them separately. The issue with his wife seems to be one that is causing you to feel insecure and afraid of how he really feels. Trust is a big issue in any relationship........while it would be a perfect world if all relationships came with a built in trust guarantee the fact is they do not. Learning to trust your partner is not as easy as some would think. The fact is a relationship is much like a project you both do together to build something. Whenever you build something with a partner you both must be on the same page and using the same directions. If you are working with a separate set of directions you are both going to come out with a messed up project. So in any relationship the couple must get on the same page with their feelings and needs.
A relationship is build on a few different things......the bottom layer is always honesty. If either party is being dishonest sooner or later the project will crumble. Next comes trust.....once both parties are being honest trust will help wrap the relationship in the love that you feel for each other. The issue you are having is trust and honesty. He needs to be honest about why he is talking to his wife and you need to be honest and let him know how this makes you feel. Keep in mind just because it bothers you that he talks to her doesn't mean that he is being dishonest.........they had a relationship. He is comfortable with that relationship and it sounds like they broke on good terms. You can let him know how this makes you feel.....but do not push him to stop the communication. Eventually your relationship will move into that relationships place and he will feel the need to communicate with her lessen. Though if they have a good friendship he may always talk to her. The key is letting him know how you feel but keeping it simple and to the point. The last thing you want to do is encourage him to hide this.
The fact that he isn't hiding it shows that he doesn't feel ashamed, or guilty over the relationship. In more cases then not when a man is cheating he feels quilt and attempts to hide the conversations. Sit down and talk to him......let him know the vague answers are not helpful and you want to be able to communicate with him about how he feels and what he needs.
As for the sexual issues this breaks down to needs as well.
Ignoring your needs is just as detrimental as ignoring his needs. We all know men can be a little hard headed and not always on target with finding and giving a women the things that she needs. But bear in mind.......we are not mind readers either. A man likes a little direction........I am not saying nag him and pound him with what he is doing wrong. But a adult conversation about what you need and want in the relationship can be very helpful for your man.
Keep in mind men are routine freaks sometimes.......maybe his last relationship she was the aggressor. Since you can not know what there bedroom habits were, you have to accept that this is a possibility. The common "He knows it is something he has to do in a relationship" bothers me a little bit.. I wonder where that is coming from? I am not a physiologist or a counselor but the comment isn't something that you would see in most normal bedroom settings. You may want to talk about this comment.
Let him know that Sex is not something you have to do. If he isn't feeling the desire to have sex he may want to speak with his doctor. It could be a medical issue or it could be something he is upset about. Either way this is something he wants to bring up with his doctor. The fact is all people are different and feel things differently. Doesn't make us sick, or off it just makes us human. If there is a medical reason then this is something his doctor maybe able to assist him with.
Talk to him.......let him know what you need. If you need him to be the aggressor then ask him to. Let him know that you are willing to switch. You may want to consider asking him what he likes in bed. (It may be that he likes a dominate women) some men like to be a little submissive in the bedroom. This could be the issue, or it could just be a routine he has fallen into from other relationships. The fact is until you both sit down and talk and open up with each other you will never know what it is he likes. It could be a certain thing he likes in the bedroom and he is afraid to broach it with you......open up about your own desires, fantasy's and needs and encourage him to do so as well. Remember the trust we talked about? Trust him enough to tell him your fantasys........even if the fantasy are something you will never do. The fact that you have them and have shared them with him will help show him it is OK to talk about his own fantasy and desires.
I would also recommend that if he is adamant with the vague answers and simply will not talk at all that you may want to consider going to a relationship counselor with him. Often a counselor can help you both communicate with each other and come to a understanding without the fear and pressures often found at home.
I wish you the best,