how did he fall out of love so fast.

im so confused.... my bf of 2 and a half years.... was witb someone when we first met.. i was totally unaware of her for the first 6 months. and i fell hard. i think we both did. they have kids together. i found out about her and we broke up.... then i found out i was pregnant but kept this from him. when he found out about our daughter he came around and wanted to be a dad... he told me they where broke up when she found out about the baby.... and he had moved in with his parents again. we made a go off things and he really really 'seemed' to have fell so so in love woth me. if ever there was a reason i felt we needed to end things he BEGGED and CRIED and told me he coulent loose me. he introfuced me to all his friends and family. and his mum even told me how much he loved me and shes never ever seen him so obsessed wnd in love with anyone before. NOW i am pregnant with our 3RD baby and within the space of a few weeks. is telling me his feelings arent strong enough to remain with me. and he run off back to his ex. seriously how does a mans feelings switch off like that???