- close friends
- best friends
- "brother in all but blood"/"brother from another mother"/"foster brother"/"soul brother" (and feminine forms using sister, instead)
I'll note that, at least in my group of associates, buddy is LESS than friend. it's someone that one willingly associates with regularly, often weekly, for some purpose, but is not actually up to friend.
Associate is of similar scope to buddy, but is work related in most connotations; in a non-work situation, it implies that they are an acquaintance with whom one has some shared activity.
Best friends isn't limited to 1 per person; its those friends with whom one shares emotional intimacy.
On the sexual score...
- one night stand - a one-off sexual liaison, often with a stranger.
- Fucktoy - crass term for for an associate with whom the relationship is exclusively sexual
- Bedbuddy - an associate with whom the relationship is almost exclusively sexual; little emotional intimacy. Often friends or buddies before the sex.
- friend with benefits - a friend, or even close friend, with whom a non-romantic sexual relationship exists.
- boyfriend/girlfriend - usually sexually and romantically exclusive relationship with building emotional intimacy. May also be non-sexual.
- partner - long term sexual &/or romantic exclusivity.
- spouse, husband, wife - legally, religiously, or socially long term pairbonded. Usually emotionally intimate, usually sexually intimate.
- mistress - sexual relationship or deeply intimate emotional relationship contrasted against an existing partner or spouse.
- other man - male equivalent to mistress, but having more negative connotations