A: Ouch! I feel for you. In relationships few things hurt as much as betrayal and cheating is definitely a betrayal. It is a betrayal of the commitment you made to each other, it is a betrayal of trust and it is a betrayal of the feelings you share. It can leave you feeling worthless and it can be a really serious blow to your ego. Cheating is a horrible thing to do to somebody you love and the after-effects can last for years and can infect future relationships. But rest assured that if you want to heal you can, the key is to want to move on from the pain and learn to trust in love again.
The very first things I think you should do is tell your new girlfriend how you feel. Open up to her and share your pain. Tell her how much your exs betrayal has left you scarred and let her know that even though you dont want to you may inadvertently be putting up a wall between you and her in an effort to keep those old wounds closed. If your new girlfriend cares for you the way you say she does she will understand and want to help you work past your feelings of insecurity and betrayal. Now that being said, dont count on your new girlfriend to heal you shes not your personal emotional nursemaid. But counting on her for support is not out of the question. In fact, in any truly loving relationship support is a given.
After laying it all out in the open for your new girlfriend and asking for her help the rest of the work is up to you. You need to remind yourself that your new girlfriend is NOT your ex-girlfriend. They are different people and whenever you feel yourself doubting your new girlfriend make a point of reminding yourself of that fact. It is not fair for you to punish your new girl for the sins of the last. Youre only human and you will slip up from time to time but you need to make a real and concentrated effort to overcome your insecurity. With time it will get easer. The deeper you bury the bad feelings from your past the harder it will be for them to keep haunting you. I know that burying your feelings is very contrary to most advice that people are given but in this case we are talking about irrational feelings and those types of feelings can be very destructive if they are allowed to run amuck. Keep them in check.
So to recap, there are three important things you need to do to get past the insecurities caused by your exs cheating. 1) Open up to your new girlfriend and ask her to be understanding and supportive. 2) Acknowledge that you were hurt by your exs behavior and that it has left you insecure about relationships in general. 3) Remind yourself at all times that your new girlfriend is not your ex-girlfriend and that until she shows you otherwise you need to trust her. Once youve faced the pain of your past you can move on. It will take work and youre likely to falter at times but in the end you can get better and learn to trust again.