While Britney Spears’ engagement to Jason Trawick imploded, her younger sister Jamie Lynn could soon be headed down the aisle. Jamie Lynn’s businessman boyfriend, Jamie Watson, tells Page Six that his three-year relationship with the young mom “is going really great” — and they’re even talking about marriage. Jamie Lynn, 21, splits her time between her sister Britney’s Kentwood, La., mansion and Nashville, where she has been trying to launch a country-music career for years. “I asked her the other night what the hell is taking so long,” Watson, 30, reveals. “But she’s really particular about her stuff. She’s trying to do it right because she knows people will be watching.”