I don't think you can. You either has to be single or married to adopt. Just living together is neither. if you are in a samesex relationship and has gone through partnership might be possible though.
Yes, it is allowed for a Muslim girl or boy to have a boy friend However; if they are of opposite sex; they should practice any kind of oral sex (kissing, touching, ... etc) or intercourse sex. They should avoid being alone in closed areas away from people. Friendship should be within the limits of advice exchange and consultation, cooperation for the community benefit, cooperation in study and knowledge exchange, social activities, .... etc. Any sexual practices (oral or intercourse) should be within licit marriage per Islam teachings and rules. It is to be emphasized that; per Islamic teachings; samesex practices (oral or intercourse sex) are strictly forbidden and not allowed.