I'm piping up to back the views of a lot of people who've already posted.
Speaking as a DFW native (now living in England), I'd be very cautious, OP. You cannot, honestly, do ANYTHING in Texas without a car. Even in Austin, where I went to uni, and which is a student town (hook 'em, horns, expat ), anything outside a very small radius needed independent means of getting around.
In all likelihood, your son will not be in Fort Worth, but a suburb. There will be very little to do, and in the best case scenario, your son will be completely dependent on the girl he's visiting to get anywhere. If she works, he will face long, isolated stretches where there's not much he can do. You might encourage him to try a shorter visit to start (say a couple of weeks?).
I understand the romantic aspect of it - I met DH when I was 23 and doing my post-graduate degree, but we dated long distance for a year, spending essentially long weekends together every six weeks (OTOH, it was pre-911, so cost roughly $200 to fly over if you waited for a good deal to come up), before we got engaged and I came over for six months to make sure we were compatible over a longer stretch of time - but I also had about 20x what your son had in the bank, good backup plans, and had been meeting my fiancé regularly over the previous year.
If it's real love, there's no rush, and there's no harm in a shorter initial visit...