Hi, I'd like to help you with your question.
You feel the way you do because you are still dealing with the trauma of what you went through with your partner. When someone is unfaithful, it creates a wound that needs to be healed through the rebuilding of trust and attention to the relationship. You need to feel special and important in the relationship. You regained your trust but it sounds like you still feel hurt by what happened. Be sure you have worked through these steps:
One, is your partner sorry for what he did? This is important, because if he does not take responsibility, you will always feel there is an open wound there between you.
Two, has your partner stopped all contact with this other person? He must do so as a first step to help you heal.
Did the two of you talk about what happened? Your partner needs to be open and honest about what he did and let you ask any questions you need to so you no longer feel on the outside of your own relationship.
If you have done all of these things to repair your relationship, then it may be that you need to do some healing on your own. Keep in mind, it takes a while to overcome an affair. You may feel that your relationship is in good shape, but you may still be feeling very hurt. Affairs can damage your self esteem badly and that can last a long time unless you can work it through.
If you feel you want help in dealing with this issue, talk with your doctor about a referral to a therapist. If you attend church, talk with your pastor. Pastors are often very good counselors. Also, if you have problems affording therapy, try your local community mental health center. They can offer therapy on a sliding scale fee system.
There are some resources that may help you:
Infidelity: A Survival Guide by Don-David Lusterman
You can find the book on Amazon.com or your local library may have it for you.
I hope this has helped you,