Ex Boyfriend claims he "changed"

my ex bf cheated on me with another girl who he had talked to for the whole year behind my back. was even calling her baby and telling her he loved her. apparently all they did was kiss but i would have never known until i read it in his snapchat messages. he lied to me constantly about being in contact with her and it was other females who be would text as well. he never stoped after i asked him countless times. i broke it off in march bc i couldn't get over all the lies. we had no trust. now that we have broken up he's changed a lot at least he makes it seem that way. he made a song for me & he cut off every girl. texts me long meaningful paragraphs every day. bought me flowers. even treats me better than before. seems like he actually cares now. but what i don't get it why he waited till i was completely done with him to be this guy i've been begging him to be for months now? makes me upset and angry. how do i know if i take him back he won't just do the same thing? i just don't know what to do with him anymore bc i still love him regauedless of everytning but i don't want him to run his little game on me anymore...