<human>: Provide a brief overview of the text.

Hey, 
I think I need some advice on fighting.
I've had a crush on a guy for a few months now and for some time it looked rather good on us ending up together.

At some point, another guy [18/m] (I'll call him B) appeared and proceeded to make his moves on my crush, winning him over. I was very defensive about this, since I did not feel I had the right to interfere with my crushs decisions, even though he had feelings for me before. I just wanted him to be happy although that quickly proved not to be the case (see below).

Two months went by in which I -unsuccessfully- tried to get over him, still keeping him as a friend. 
I never thought the two fitted and had the strong feeling, that B was hurting my crush emotionally since they were together (he started full on smoking again, for example), but I know very well that I cannot really trust my perception on any of this.

However, lately, I heard from most of our mutual friend that they don't think their relationship will last much longer and that they noticed him being unhappy/stressed out as well. 

That, combined with the fact I really can't let him go even though I tried, lead to the decision to fight for him.
Now, I won't do anything to drive them apart. I really wouldn't have the right to (although, in retrospect that was exactly what B did) and it wouldn't really help either.
But I want to be present and, when their relationship ends, try to win him over myself.
Question is: What is the best way to do this? Any advice?
<bot>: My crush has another boyfriend, everyone is expecting that relationship to end soon(ish), how to best get to him?