If you have a boyfriend that use to love you, and he just stop loving you what should i do?

me and my boyfriend been going pout for 6 months, for valentines i thought we was going out, he daint call me to say happy valentines day. i called him and wish em. than he stop talking to m, whenever i call he aint pick up ma calls. and i find out that j\he cahange number cause he daint want me to call him. i wanna konw what to do cause i really love him.