If she's engaged to someone else and gets jealous when you go out then she cant be that happy and contented with the guy she's with. Either way dont get stuck in the friendship zone, either do her or get out of her life, its not fair on either of you if your kidding yourself that your "mates" when in actual fact she's a girl you wanted to fuck, but it went wrong somewhere down the line, and now your stuck in platonic hell. Its hardly fair on her if your hanging round in the background of her relationship like some sexual tension magnet.

Do what I do and learn NLP, then you can satisfy your base urges by having shallow cheap unfulfilling lovless no-strings sex with dozy women who get mezmerically bamboozled easily. The best bit is all you have to cope with are the feelings of guilt and self-hatred the day after, instead of the months and months of "will she, wont she, are we mates or does she like me, but does she like like me, but what about her ex etc etc" swimming around in your fucking head. Much better way of doing things.

God I'm fucking lonely