Is it illegal for a 17yo to sleep with a 15yo in Missouri?

I'm 15 and my boyfriend is 17. We don't plan on having (he wants to wait) but his mum has been insistent on attacking the two of us over the issue of him going to prison or becoming offender if we have and get caught. I've read up on the missouri laws and I know it says anyone under 21 can sleep with anyone as young as 14 but when we mentioned that to his mum she says it only applies to heteroual couples and that because we are both guys it's consider sodomy unless we are the same age..so that's my question can 2 gay male teens have in missouri if one is 15 and the other is 17?