If I do eventually contract and become a Second Lieutenant, I will have to serve on Active Duty, right?

No. At least two-thirds of the upcoming graduating Cadets will receive an active duty tour. Cadets who receive Reserve Duty will serve in local Reserve or National Guard units one weekend a month, or serve in the Ready Reserves with no "drilling" requirement if a suitable unit is not available where you reside. The Reserves are one of the best adjunct career and retirement systems in the U.S. today.