Lets get sure, that you really feel sorry. Look at her and attach a nipple clamp to each of your nipples and leave them there until the end of the therapy session or told otherwise. Now say the following to her and don't forget to stroke for each word:
"<friend's name>, I am sorry for all the painful frustration I have caused <ex's name> by not being able to give her a real orgasm."
Do you feel the frustration? Repeat 3 times.