I recently got back taling to my ex and we started to have sex again but for some reason I seem to not be able to keep an erection with her everything feels good and I want it to happen but if we start to have sex and I stop between to give her oral sex I go soft and can't seem to go erect again during the time we were apart she seen other men I was wondering if maybe I'm thinking that maybe she isn't enjoying being with me I'm kinds of disapointed in myself for it and she is also I don't know what is wrong any ideas?

I forgot to add that before I stop to give her oral I am about to ejaculate could this also be the reason for me going soft I'm losing my sensations and feelings?

It could be that you are close to the point of ejaculation. However, you should see a doctor to see if there is anything Physically wrong with you. Just in case.