Rihanna has admitted she doesn't understand love.The 'Stay' singer - whose relationship with her on/off boyfriend Chris Brown is reportedly on the rocks again - hinted that all is not well with their romance on stage in Los Angeles on Monday night (Apr 8).The 25-year-old star, who is currently on her 'Diamonds' world tour, asked the audience: "How many of you are in love? How many of you hate love? How many of you don't f**king understand it? I'm in that group."According to People.com, she then began singing the track 'What Now' from her latest album, the lyrics of which include: "I've been ignoring this big lump in my throat/I shouldn't be crying, tears were for the weaker days/I'm stronger, now what, so I say/But something's missing."The Barbados native has been finding it difficult to see 23-year-old Chris, who is gearing up to release his new album 'X', because of their busy schedules.The couple - who reconciled last year even though Chris is still on probation for beating her in 2009 - were spotted partying at different Los Angeles hotspots over the weekend but friends insist they are still together and just have a lot going on.A source previously said: "Chris ain't trying to hear no nonsense today. It's simple, he with Ri. "They're cool and if and when something changes, between them that's between them - they both have a lot going in their careers right now and just doing them and focused on they work."They've been trying to connect but it hasn't been clicking for them. It ain't like Rihanna got time to just chill and run through - she's on tour and her schedule is way too tight."