I would trust them, for two reasons:

1) girlfriendSSSSS - in plural. If it were one girlfriend, one could suspect all sorts of ulterior motives, but with girlfriends in plural, you gotta trust the wisdom of the crowds.

2) surprised is an authentic reaction. they are not trying to talk you into leaving him - they are surprised (raised eyebrows and an expression of disbelief on their faces, probably?). Because the reaction is authentic, likewise, I would not suspect ulterior motives but trust the judgment of outsiders who are more objective.

The bf appears out of touch with reality in saying that he has no problems and his life is wonderful. Most people would realize that they are not perfect and that there is room for improvement in their lives.