I would as long as i didn't feel threatened by him. And in most cases i wouldn't feel threatened. You say bullshit like this "Him and i went to chilli's" - is the polite way of saying, "he and i didn't go out to chilli's, we just went somewhere and fucked" .. and that's being real, sorry if that sounds rude or out of line, but i think you need to hear it how it is."
Which is why im calling you a moron. Come on that is bullshit and it shows you aren't very experienced with girls and have no idea how they think.
If a girl is with you, in a relationship, but there is another guy who has confessed his feelings for her and she rejected him even BEFORE she met you then this guy will for sure have lower value than you. As long as you just maintain that value she will never ever feel any sexual attraction for him and would never risk your relationship for him. Sure this could happen if you neglect her too much but most likely she will find some random guy and not someone she has been talking to and using for favors for a long time.
He is just some white knight that she can call when she needs a ride because she knows he will do what she asks him to, he means nothing to her.
I'm agreeing with most of your logic here, but on the real - if OP has said to his girlfriend, "nah - im sorry, im not comfortable with you hanging out with this guy" and she's brushed off his opinions and put this guy before respecting her own boyfriend, what does that say? why is THIS guy so important? Because she can exploit him? How is that an attractive quality .. although you're right, my bad for, "they didnt go to chilli's, they probably just fucked". But i did say, it's either she's cheating or she's using the other guy.
I'm not going to get into a "my dick is bigger then yours, i've fucked more girls then you" teenage type of arguement, but i'm plenty confident with women. I'm 25 and i've been around enough women to know the difference between a girl that respects people, and girls who will do what they want because they think it benefits them.
My girlfriend would never hang around with some guy that had admitted "love" feelings for her, not because of how i might percieve it, but because ultimately - if she doesn't feel the same, she effectively see's the friendship as ruined. It WOULD be different - if OP's girlfriend and this guy were best-friends, then one night he let slip he really liked her, she said no, but the guy just took it in his stride and continued wanting to be a friend... but that's not the situation at all. She's all about doing her & either using this guy or completely disrespecting OP.