My wife has never gotten the diving bug in over 25yrs. of marriage. Hence, until my son started diving this summer, I mostly went solo or with an "insta-buddy".
While I've had some pretty bad experiences with insta-buddies, for the most part it was because I 1) Didn't tell the DM/Cap'n what my needs were or 2) I was participating in something (like photography) that my new buddy did not have an interest in doing/watching (there's nothing like hanging around ONE coral head for the entire dive if you have no interest in the critters there.)
On the other hand, it's been a rewarding experience more often than not. On one trip, I found a dive buddy who traveled with me on dive trips for several years (Cayman, Cozumel, Roatan). On others, I got to see the joy of a new diver as he saw the ocean from underneath for the very first time.
Don't be afraid to hook up with an insta-buddy, but take the good advice offered here earlier: Let the DM know you are new, then ask if he can find an EXPERIENCED diver he knows or would recommend to you (in most places I go to in Florida, the DM's know several of the divers on the boat and they usually know the trip leader, if he/she is from out of town.) If he hooks you up with an insta buddy, TALK to him. Look at his gear and his setup and ask about his dive plan. Make sure if he's on a computer, you are too. If he's on the tables, you must be willing to dive tables, too. (I made this mistake once. After a really long, deep dive, I asked my buddy how close he came on his computer, since mine used an old algorithm. "What computer?" . His "computer" was dive timer. He was so far off the tables at this point I refused to make the next dive with him.) My BAD, a big OOPS. From that moment, I always asked.
If, after your insta-buddy review you aren't comfortable, go back to the DM.
If no experienced diver is willing to help a neophyte, or you get the willies after talking to them, be prepared to ask for a guided dive with the DM (pay/tip him well for this). If you demonstrate some good skills, the next time out, you'll find the DM will be more helpful in finding you a good insta-buddy, as he has assessed your level of skill--or then again NOT, if you tip too well.