Boyfriend and parents dont get on, help?

My boyfriend and I discovered I was pregnant a few weeks ago(my boyfriends 19 and i'm nearly 17), i aborted the baby(i don't half regret it but what's done is done) and my parents now hate my boyfriend. Its more my step-dad than mum, she easily forgives but he holds grudges like there's no tomorrow. And he apolized to them a lot and my step-dad says if he see's him again he won't be held responsible for his actions. The fact is, is it's my prom tomorrow, and I want my boyfriend to see me before I go, but my mum recommends me not allowing my boyfriend to see me because my step-dad will be there? I'd much prefer my boyfriend to be there than my step-dad but that won't happen. Any advice?