This one's tricky, and all too possible for there to be no good outcome. I wish Prudie would have emphasized more that both of them have suffered some really big traumas related to their mothers. Really big, and really incompatible. LW can try to see their girlfriend's love and warm relationship with her mother, and then the trauma of the loss, and not try to be jealous, envious, etc. And the girlfriend can try to see LW's fraught relationship with their mother, and the fact that it's not LW's fault and healing may have to come from the mother. But it's also entirely possible that both of these are insurmountable mountains from the valleys of the traumas they're both in. I feel for both of them. It may be that they can stay together, not really prodding the mother angle, but if they do, I'd really encourage both of them to get therapy or find another close friend/partner/etc. that they can talk to about their mothers, without the minefield that each has for the other. This is not something that is ever going to go away.