There are enough students at Pitt to make a smorgasbord of potential relationships, whatever type you're looking for. The student body varies widely, though girls are almost always considered better looking. Pitt men have much less to complain about than CMU students up the street because they have many more options available. On the whole, the campus isn't especially notable for the amount of romantic interactions. While relationships aren't uncommon, they also aren't by any means the rule. Casual dating and hookups are frequent, especially during the first couple of years.
Most students find that it's not hard to find a great group of close friends at Pitt. With people from so many walks of life, it's no surprise. By the end of the first year, many people already have their future roommates picked out and have usual places and activities that they do. Pittsburgh is known for being a friendly city, and many are hard pressed to want to leave Oakland. The best advice is to meet as many people and do as many things as possible, especially in your first year. It can take some time to get settled in, but once you do, you'll likely find yourself surrounded by people who you genuinely good friends.