You got to admire Marge for her assessment of Tom (in a letter to Dickie):
If you want to make some changes for your own good, for gosh sakes get him away from you. All right, he may not be queer. He´s just a nothing, which is worse. He isn´t normal enough to have any kind of sex life, if you know what I mean.
And finally Tom gives us a glimpse what he is really good at:
(After having acted like Dickie for quite some time) It was a good idea to practice jumping into his own character again, because the time might come when he would need to in a matter of seconds, and it was strangely easy to forget the exact timbre of Tom Ripley´s voice. [...] Sometimes, if the song in the radio was one that Tom liked, he merely danced by himself, but he danced as Dickie would have done with a girl [...]
He had done so little artificially to change his appearance, but his very expression, Tom thought, was like Dickie´s now. He wore a smile that was dangerously welcoming to a stranger, a smile more fit to greet an old friend or a lover. It was Dickie´s best and most typical smile when he was in a good humour. [...] Wonderful to sit in a famous café, an to think of tomorrow and tomorrow and tomorrow being Dickie Greenleaf!