@LocalHobo
But you are not his Mother?
I don't understand why my DH would get me a gift for Mother's Day. Once your DC starts nursery you will be overwhelmed with scribbles and tat. That is what it's all about with little ones, not expensive gestures.
Exactly this.
The post from OP comes across as very self preoccupied and insecure. OP is very jealous her boyfriend is spoiling his mum on mother's day, but this is what he should be doing since she's his actual mother(!!) 
She carried him, gave birth to him, brought him up from baby, has there for him in every way well before OP came on the scene, and has been a vital part of his life since he was born, and obviously still is. That's what the day is celebrating and OP you're simply none of those things in relation to him. Calm down and stop seeing your MIL as competition.
Romantic relationships, especially unmarried ones, break down all the time. In the future, you and your boyfriend may break up, but she'll always be his mother no matter what, and this is the key named day in the year to celebrate this unique bond. Wait until your own kids are older and i'm sure they'll celebrate with presents etc.
Also why the focus on materialism and wanting to arm twist people into providing presents they don't want to give? Why not be satisfied with a genuine well wish on mothers day from him instead of expecting all these things when you're not his mother? All this jealous and unreasonable behaviour will be really putting him off you and will only backfire on you.