Am i wrong to be upset?

I fell pregnant last year only 8 weeks into a new relationship.we split up when we learned of the pregnancy but the father promised to be a part of the babies life.sadly I had a missed miscarriage at 12 weeks and I haven't seen him since the day after the d&c...within 2 weeks he was seeing someone else and hasn't contacted me since.fast forward to the other day to what should of been baby's due date,i waited all day for him to text,call...anything to acknowledge our little angel but nothing at all from him! I know I'm going to bump into him at some stage (he's my brother in law's best friend) and I'm just not sure I'll be able to be civil to him when I do.am I just over reacting though by being annoyed about it?