Why?

Today my mom told me that my sis Evelyn tell her my bf Ken ask her to be his girlfriend for 1 day before...at the moment I was stunt and don't know how...just thinking is is a joke? She told me is real,some more she said Ken love another girl also when I was together with him...we always argue is because of her...

Before that my friend that working with the girl she told me before..that time I also ask before Ken but he say don't have this thing happen,because the girl is already got bf and he no love her before..but now my sis told me that he bring her go the girl shop before and said he love the girl before and wan to chase her...

Why suddenly I can't think about anything..I don't know who say is true or false...

Actually many times i already choose to trust Ken..but the same thing like keep on forcing me to suspect him..I really don't know what for my sis wan to lie me...

I suddenly think back last time he did many thing I also choose to trust him...just like last time in friendster he wrote a testi for a girl and wrote love ya and miss ya...after the argument I still choose to trust him..I really started to think am I choosing the right way? I very confuse and headache...when I thinking back all the thing I really very suffer..why keep on like that? Does ken really do that before? I hope and I wish the answers is not..but in another way I also trust my sis...how? What I suppose to do now?

I really very angry till I have nothing to say...really don't know what to say...now is my sis told me this not other people..why will like that? If this thing is real what I need to do?