As I preface any piece of advice: only you can decide what is best for you, don't let anyone else convince you what to do. Also, I'm assuming you're also wisely seeking advice from peeps who know you in real life.
That being said I'll repeat the decision process I've shared elsewhere on the forum:
1. Are you planning on getting married?
If your answer to 1 is yes then proceed to 2. If it is no, then stop. I don't see any point in having a long distance relationship if there is no long-term plan. The reason I think this is important is that in general if you ask a female to somewhat alter her career to move to your city and then you end up being meh about long-term commitment once you are in the same city, the woman usually doesn't take kindly to that.
2. Can you handle a LDR? You two probably should have an honest conversation with each other about expectations and your ability to handle a LDR. Also, in reference to question 1, you should lay out the game plan for getting married so that you two are not in limbo during the LDR.
3. I'm assuming both of you are Texan. In which case, what's the big deal? lol. That is a 3.5 hour drive tops with traffic...usually much less especially if driving from central Houston to central SA...in Texas time/distance that's like an afternoon drive in the park. But seriously, in terms of LDRs that's not that big of a distance. You should have a discussion about number 2 above but in all reality most serious relationships should be able to survive a one year LDR with a distance of 3.5 hour drive. Plus, since you'll be an intern there won't be much difference between being in the same city and in different nearby cities. Even if your SO were in the same city you wouldn't see her that much except free weekends. In the case of a LDR you would still see each other on your free weekends.