My son hates me

My 5 year old son told me he hated me. Our relationship was fine until I accidentally got pregnant with my now bf. Once I introduced them my son has been bitter and jealous, even of the new baby. He won’t say a word to my bf, gives us both an attitude, etc.

back story - My 5 year old sons dad and I broke up 3 years ago. He cheated, was abusive and just a terrible person to me. He never wanted or still never spends time with our son. On his days, he ALWAYS takes him to grandmas so he can go do whatever he wants yet he says I never see him cause of my work schedule which is ridiculous cause I have him every minute I’m not working.

Is there anyone out there that can give me tips on how to get my son over this? It’s not his fault, if anyone it’s my fault.

He will say “well grandma lets me do this and grandma lets me get that” grandma is the babysitter and where he spends his other half the time. She doesn’t work so she can go do whatever whenever, spoiling my son. So when I can’t buy what he wants or do what he wants he gets mad at me.

But mainly I need to figure out how to improve my son and bfs relationship. My bf is nothing but good to my son but it’s almost to the breaking point. He won’t even come home now cause my son gives him an attitude nonstop.