C..
well, yuck.
Here is what I would say:
Take the Lexapro. It will take a few weeks to kick in and, although many anti-depressents have the suicidal thoughts side-effect warning, it's quite rare. It's only in about 1-2% of all the people who take them. So for every 100 people under 18 - 3 or 4 will have suicidal thoughts... but 2 of them were ALREADY suicidal, so the actual "risk" of taking the anti-despressant is no more than 2%. That is small compared to the 96 that feel better as a result of taking an anti-depressant.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3195160/
That will take a few weeks to "kick in". In the mean time:
1. No more girls. Have him make a "pact" that a girl is not the answer and he will not 'date' for the remainder of the school year. This will buy him some time to re-create his behavior and look at why he is choosing lame girls who cheat on him.
2. Find an individual counselor. If he is going to family counseling then he needs his VERY OWN counselor who is in HIS corner and can advocate for HIM.
3. Get him involved in an activity. Tae Kwon Do or swimming. Something where there is an "individual" component but he has a "coach" who is giving him positive reinforcement.
4. Find an actual "mentor". Big Brothers or boystown or something. There are mentors who can spend time with him and show him what a positive role model is like to be around.
5. Friends - if you get him into an activity that he likes (or at least one he doesn't hate) he may meet a friend or two that have the same interests.
6. Does he have an outlet for his anger? If he's angry all the time.... what is he doing about it? Have you talked him through appropriate things he can do? Like exercising or boxing bag? so that he knows he can have a predictable routine when he starts to get mad?
I hope things get better. It sucks to see your kids not doing well.