When should i tell my boyfriend I'm pregnant?

Completely confused as to what to do. I'm 18, in my first year at uni which i've worked so hard to get here for... and ive just found out i'm pregnant. oddly... im happy about this mistake. I've always wanted children, and although im scared and nervous, im looking forward to it, and im willing to give everything up for this baby. However my boyfriend is only 22 himself, and already has a son from his previous girlfriend... hes alslo going through alot at the moment, hes just lost his job, his ex wont let him have access to his son, hes hardly eating and i think hes suffering from depression. i fear that by me telling him im pregnant it will make things so much worse. Im really close to his mum, and im considering telling her first, but do you think my boyfriend will begrudge me for talking to his mum before him? please help. I feel so helpless. Thank you.