When he tells you he wants to see your cell phone, he is most likely checking to be sure you are not cheating on him. Keep in mind that he is doing some pretty awful things to you. In the back of his mind, he may be fearful of you cheating on him. Although he is doing these things because he feels he is the center of your relationship, he still has insecurities. Otherwise, he would not be doing what he is doing to you. A person with a good self esteem does not need to think of themselves all the time, cheat on their partner or make an issue out of anything, especially seeing their partner's cell phone. If you want to maintain control of the situation, do not let him have your cell, even if you are getting rid of it. Instead, donate it to a women's shelter (they use it to help women in domestic abuse situations) or call another charity to see if they can use it.
Since you mentioned the sex issues to your boyfriend, he is holding back to maintain control. Instead of doing something about it and working on it with you, which would be a healthy response, he is using it to control you. He knows that it bothers you. In order to deal with it, it might be a good idea to drop the topic all together. Refuse to sleep with him. Just act as if it doesn't bother you. He may try to approach you more often about it, but keep saying the same thing- "I'm not interested". If he wants to know why, tell him. But then go right back to saying the same thing when he talks about it.
The girl he is fooling around with who is friends with his aunt may know that you are together, but she wants to feel she can take your partner even if he is with you. People who try to move in on a relationship with the intent of stealing someone's partner almost always have a very low self esteem. They feel that the "thrill" of having someone else's partner means they are special and better than the other person. Your partner also feels it is a thrill to do this under his aunt's nose and get away with it. It probably makes him feel he is superior since he is getting away with it. The only real way to beat this is to leave him. He is going to continue to cheat as long as he has the issues he has and has no insight into his problem.
If he is going out on Fridays, there is no reason for you to wait around for him. He is not informing you of his plans and he is also canceling your plans with him. This is basically putting you in the back up position, which as his partner is not fair to you at all. He should be treating you at least equal with himself. But instead he is putting you last. That means you do not have to put him first. Not for the sake of revenge, but for the simple fact that you deserve to enjoy your Fridays as much as he enjoys his. Make plans and stick with them. If he knows you are going out, he may change his plans for fear that you are cheating on him but keep your plans anyway. Let him know that when he is ready to keep his dates with you, you will go out with him. Otherwise, you are sticking to your plans.
To get mentally healthy again, you can focus on increasing your self esteem. Start by learning more about how you can feel better about yourself. Here is a link to help:
And here are some books:
Self-Esteem: A Proven Program of Cognitive Techniques for Assessing, Improving, and Maintaining Your Self-Esteem by Matthew McKay and Patrick Fanning
Healing Your Emotional Self: A Powerful Program to Help You Raise Your Self-Esteem, Quiet Your Inner Critic, and Overcome Your Shame by Beverly Engel
The Courage to Be Yourself: A Woman's Guide to Emotional Strength and Self-Esteem by Sue Patton Thoele
By learning more you about feeling better about yourself, you can begin to work your way out of this relationship and into a healthier one.