Why didn't Lenny accept Melissa right from the start.

Even when Lenny was a loser working for Max at his Burger Joint and many others didn't treat him well, he didn't need Sharon to begin with. Yes Rafferty told Bobby that Lenny felt nobody cared for him, but even when the rest of the school or most of the town wasn't accepting him,(not hating him) he could have accepted Melissa's friendship all along to begin with and she welcomed him into her too and why didn't Lenny realize that to begin with? Its confusing. He only realizes that after his second date with Sharon when she leaves him at the party to dance with two other guys.

Plus Lenny wouldn't have had problems with Fred Gallo or McIntryer if he just kept Melissa while she was his co-worker not go toward Sharon and Lenny should have had common sense that at the time Sharon was in a relationship with Fred Gallo so shy couldn't Lenny just have Melissa and be happy and even with the world against him at that time Melissa would have shared it with him. Not Sharon.