If I was single and in SA for the weekend I'd consider the following:

To be honest I'd probably be in New Braunfels floating the Comal River for the weekend. Major party but probably not what you are looking for.

In SA the Alamo and central riverwalk are interesting but will be CROWDED. Go early or late to avoid the crowds. When you're downtown don't miss San Fernando Cathedral.

The Museum Reach (north) section of the riverwalk will be much less crowded and for me it's more interesting than the touristy section. Walk it if you have time or take the river taxi. Along the way stop across the river from the SOMA and grab some lunch at The Luxury At the northern end is the Pearl Brewery complex with great shops, restaurants, and entertainment options including two of the best restaurants in the city (Cured, Il Songo Osteria). Don't miss Bakery Lorraine for pastries and JazzTx for cool late night sounds.

The Mission Reach (southern) section of the riverwalk is also interesting but much less commercially developed at this point, It does link to all the other Missions (UNESCO World Heritage site) if you're interested in the history of the area. If you only go to one mission I'd suggest Concepcion or San Jose

Beyond the central core of the city are several other areas of interest.Southtown is an up and coming area full of historic homes and foodie hot spots. Try Bliss, Feast, or Hot Joy

Northwest is the La Cantera/Rim area with some of the best shopping and entertainment options in town including Six Flags Fiesta Texas, Shops @ La Cantera, Elian, and The Rim. UTSA is also in the area so lots of single college aged Texans to mingle with.

Stone Oak area north of town is where the SA Temple is located. It's a huge suburb with some good dining options but not a lot of sites to see. Several Cougarboarders live up there so be warned.

BM me if you have questions or want more details. Have a great time in SA