Monster in law

So my boyfriend mom hates me . We got along very well until i got pregnant . Yes we were only dating for about 10 months but we are 29 years old both have good jobs we now live together in a house and never ask her for anything . He does have another son 3 years younger then ours but when she found about him she didn’t react nearly as bad when we told her . She told me I ruined everything told her son she disowned him along with many many other hurtful things. This was very hard for me because I was only 2 months pregnant. Our son is now 2 months old n she has very little to do with him has only come to see him once . Yet she is constantly taking is other son out n putting in time with him . She makes it very obvious she doesn’t like me and things get very awkward. I love this man more then words can explain but I feel like because his mom hates me he will never purpose me. I don’t know what to do about his mom anymore it hurts he to know one day I’m going to have to explain to my son why his grandma favors his half brother over him .